Despite its seeming zaniness, "The Smithsonian Institution" is appealing in several ways. First, there is the simple suspense of T.'s adventure: Will finding the right past to change really make a difference? Then there is the science-fictional illusion that Vidal successfully creates. Despite a certain amount of mumbo-jumbo, you come to believe in the novel's world of intersecting realities, where all time collapses into a quantum present and individuals meet different versions of themselves along the space-time continuum.

''The Smithsonian Institution'' is a light entertainment to while away a winter weekend; it will go on no one's short list of Vidal's best books. Most of the details, including the erotic romp of T. and Mrs. Cleveland, wouldn't bother the age- 12-and-up audience recommended on my copy of ''The Time Machine.'' But the jokes, good and bad, keep coming, and the Presidents really are brought to life. Vidal's eye for the freaks and foibles of Washington has retained its sharpness.

"Girl in Landscape" -- which could be called science fiction for those who like that sort of thing, although it shouldn't scare off those who don't -- uses the raw materials of those fears (mysterious viruses that change our perceptions; dry, spooky terrain that looks like nothing so much as nightmare territory; tiny, slimy creatures that grow inside of potatoes) as a way of exploring both the awe of female adolescent sexual awakening and the treachery of it. ...

...even when Lethem uses the language of science fiction to shape his story, he doesn't have to stretch to make his fantastic metaphors work. He knows adolescence is its own kind of weird tale, and if the fear of it wasn't exactly what kept us awake all those childhood nights -- well, maybe it should have been.

Someplace to be Flying is also a solid thriller, full of suspense and peppered with villains of various talents and their adversaries, the decent folk who constantly try to thwart their evil intentions. Though De Lint may be a master of contemporary fantasy, he also brings to life the human frailties of his characters and the spirit with which they cling together: "What I do know," says one character, "is that we've all got our hidden currents, no matter how wide and friendly the river seems. Start casting deep enough and who knows what you'll dredge up." The reader does not have to be strictly a fan of either thrillers or fantasy to thoroughly enjoy this delightful tale.

Readers who prefer neatly ordered narratives and precisely delineated characters will do well to avoid the nested levels of ambiguity that are Jones's stock in trade. But a tolerance for uncertainty seems appropriate in any thoughtful exploration of alienness. Anyone willing to take up the challenge should read this trilogy from the beginning.

This is science fiction with an emphasis on science. Egan makes no concessions to readers who cannot decipher, or least comfortably bypass, sentences like: ''Some shriekers sent out metronomic bit-streams; others produced pseudorandom stutters.''

He has included many fascinating details about ant biology and ant society. But his efforts to dramatize this material verge on the amateurish.

Its Victorian version of science fiction manages effects that are rich and Gothic yet somehow innocent of irony. We may ascribe these effects to self-conscious literary echoes, tongue-in-cheek post-modernism or the desire to tell an old-fashioned adventure story: the novel works on all levels. It seldom creaks or groans beneath the weight of its devices, and its flair for description can be positively Dickensian. The result is a fresh take on an old formula -- the dystopian postapocalypse novel -- and a profound meditation on the nature of time.

There is much that is fantastical about Fowler's fiction, but also much that is rooted in a solid emotional reality; in fine-edged and discerning prose, she manages to re-create both life's extraordinary and its ordinary magic.

Beehive is a straightforward thriller that moves Carroll away from the magical darkness of his eight previous novels, the best of which — such as Sleeping in Flame or Outside the Dog Museum — truly defy characterization in their themes and imagery. ...

There are wonderful touches, though. Two of Bayer's books, for example, are titled The Tattoed City and The Magician's Breakfast, which sound like stories Jonathan Carroll would write. Carroll's characters get defined in his normally quirky, yet irresistible fashion. When we first meet Bayer, he tells us: "I do not like to eat alone and this is one of the reasons why I became famous." ...

But the best reason to read Beehive is to know, throughout, that if you like this even a little, you will love the rest of Carroll's canon.