We examined in vitro the effect of several drugs on the activities of lysosomal enzymes in the crude extract of bovine retinal pigment epithelial cells. Acid phosphatase, beta-D-glucuronidase, N-acetyl-beta-D-glucosaminidase, alpha-L-fucosidase, and alpha-D-mannosidase were used as lysosomal enzymes. Sodium iodate at 10(-6), 10(-5) and 10(-4) M, and potassium iodate at 10(-5) and 10(-4) M inhibited acid phosphatase activity. Ferrous chloride at 10(-5) and 10(-4) M suppressed beta-D-glucuronidase activity. Ferric chloride, indomethacin, chloroquine, chlorpromazine, 5-fluorouracil, tobramycin, daunomycin, oxalate and epinephrine had no or only minimal inhibitory effects on the lysosomal enzyme activities examined.