AMENDED: An 80 mcg dose of gp160 has been chosen for the booster because this dose has been shown to be safe and immunogenic in previous trials and allows comparison of the late boost in this protocol with the late boost in the protocol in which patients were primed with three doses of gp160. Original design: HIVAC-1e vaccine is a preparation of the envelope protein of HIV (the virus that causes AIDS). The protein is produced by genetic modification in vaccinia virus. The purpose of a vaccine is to produce an artificially increased immunity to a particular disease, in this case, AIDS. Since there is no known cure for AIDS, the control of this disease necessitates the development of effective prevention such as vaccines.