The effects of cimetidine (400 mg b.d.) and ranitidine (150 mg b.d.) on high-density lipoprotein (HDL) subclasses and other plasma lipoproteins were studied in 18 men and 15 women with reflux oesophagitis and/or duodenitis. Serum testosterone and sex hormone binding globulin (SHBG) concentrations were also measured. Treatment with either drug was continued for 12 weeks. Ranitidine had no significant effect on any measured variable in either men or women. Cimetidine had no effect in men, but in women it raised the cholesterol concentration in the HDL2 subclass by 15% after 8 weeks, and by 48% after 12 weeks. In females, cimetidine also reduced the concentrations of SHBG (by 24% at 12 weeks) and of total testosterone (by 25% at 12 weeks). The significance of these latter changes is uncertain, however, as estimates of the biologically active free testosterone concentration were unchanged.