To determine the safety and maximum tolerated dose (MTD) of 2',3'-dideoxy-2',3'-didehydrothymidine (d4T) administered to patients with AIDS or AIDS related complex (ARC) who are intolerant of zidovudine (AZT). The study also begins an assessment of the effectiveness of d4T therapy on HIV replication, on plasma levels of p24 antigen, and clinical or immunologic parameters associated with AIDS.