Human spermatozoa were incubated in vitro in the presence of α-chlorohydrin at concentrations which inhibited motility, but which were not spermicidal. The inhibition of motility was not reversed by washing or by addition of α-glycerophosphate. Metabolic activity of the spermatozoa was reduced, as measured by glucose, oxygen uptake and lactate production. Endogenous respiration was not affected. Cyclic AMP levels were reduced. Thus, at least part of the adversed effects of α-chlorohydrin on male fertility may be due to direct inhibitory action on the spermatozoa.