Ecologists and toxicologists are concerned with the presence of pharmaceuticals and personal-care products (PPCPs) in urban aquatic ecosystems. Cimetidine (H₂ histamine antagonist) and caffeine (stimulant) are two common PPCPs found in U.S. streams. Histamine has been shown to regulate invertebrate olfactory and stomatogastric functions and caffeine has an antagonistic effect on cAMP and adenosine. We predicted that exposure to these two PPCPs would affect the metabolism of Procambarus clarkii (crayfish). Cimetidine was administered to crayfish through food, as previous data show that cimetidine readily sorbs to organic matter. Caffeine was administered directly into the water column, as it is relatively stable in water. Over 6 weeks, we measured growth, egestion and basal metabolic rate (BMR). We measured growth using wet-weight and found no effects of cimetidine or caffeine on growth. Egestion also did not significantly differ among treatments. BMRs for high-doses of both PPCPs were not significantly different, but tended to be lower than control. BMRs for low-dose treatments were statistically lower than the control after 2 weeks, (ANOVA: cimetidine p= 0.010; caffeine p= 0.016), but not subsequently. These experiments did not indicate a consistent significant effect of PPCPs exposure on growth, egestion or BMR of crayfish.