When ejaculated ram spermatozoa were incubated with (S)-alpha-chlorohydrin (up to 0.25 mM) the oxidative metabolism of fructose to carbon dioxide was inhibited in a concentration-dependent manner. This appears to be due to inhibition of glyceraldehyde-3-phosphate dehydrogenase which leads to the accumulation of fructose-1,6-bisphosphate, dihydroxyacetone phosphate and, to a lesser extent, glyceraldehyde-3-phosphate. (R)-alpha-Chlorohydrin (10 mM) had no significant effect on the oxidative metabolism of fructose. The inhibition of the oxidative metabolism of fructose by (S)-alpha-chlorohydrin (0.1 mM) was not immediate but was detected after incubation for 15 min. By contrast, (R,S)-3-chlorolactaldehyde (5 mM) caused an immediate inhibition of this metabolic pathway. 1-Chloro-3-hydroxyacetone (0.5 mM) immediately decreased the oxidative metabolism of fructose which resulted in the accumulation of key fructolytic intermediates in a manner comparable to that produced by (S)-alpha-chlorohydrin. At a concentration of 20 mM, 6-chloro-6-deoxyglucose had no significant effect on the metabolic activity of ram spermatozoa. We suggest that the anti-fructolytic actions of (S)-alpha-chlorohydrin and 1-chloro-3-hydroxyacetone are mediated via a common metabolite, (S)-3-chlorolactaldehyde, and that the inactivity of 6-chloro-6-deoxyglucose is due to the inability of ram spermatozoa to metabolise this chlorinated sugar to (S)-3-chlorolactaldehyde.