Many patients with AIDS have gastrointestinal complaints, including the major clinical disorder of chronic diarrhoea. The pharmacokinetics of zidovudine was studied in 9 male patients with HIV infection and diarrhoea to establish whether drug absorption was impaired in them. The peak plasma concentration and AUC after a single oral dose of 200 mg, were the same as those reported in 6 healthy male volunteers (3.1 vs 4.0 mumol.l-1 and 7.2 vs 5.2 mumol.h.l-1, respectively). Since the bioavailability of zidovudine is not particularly impaired, oral zidovudine therapy can be maintained in patients with diarrhoea.