To assess the safety and tolerance of multiple oral doses of nevirapine in combination with zidovudine (AZT); to get information on the pharmacokinetics (blood levels) and dose proportionality of nevirapine/AZT with multiple dosing; to characterize the pattern of virological activity in vivo (in humans) of nevirapine in combination with AZT; to determine whether development of resistance to either drug is slowed by the use of the combination.