After modulation of sulphation and glucuronidation, the relationship between the changes in metabolism and cytotoxicity of chloropropham (CIPC), a widely used herbicide, was investigated in isolated rat hepatocyte suspensions. Under physiological conditions, CIPC had a cytolytic effect, modified membrane permeability and reduced intracellular ATP level. CIPC was metabolized by hepatocytes mainly into 4-OH chlorpropham sulphate (37%) and glucuronide conjugates (18%). Inhibition of sulphation, by omitting sulphate from the isolation and incubation media, did not affect the cytotoxicity of CIPC, since there was a 2.5-fold compensatory increase in 4-OH CIPC glucuronide. Inhibition of glucuronidation by adding 4 mM D-galactosamine in the incubation medium led to a 66% decrease of glucuronide conjugate and simultaneously to a 32% decrease of sulphate conjugate. In that case, concentrations of free 4-OH CIPC in both hepatocytes and incubation medium were markedly increased, while those of 3-chloroaniline and 3-chloroacetanilide were slightly modified and remained low. This alteration of metabolism was accompanied by modification of cell permeability and reduction in ATP synthesis. The cytolytic effect was due to CIPC itself, whereas the effect on energetic metabolism was attributed to a metabolite. Results demonstrated for the first time a partial inhibition of sulphation by D-galactosamine (4 mM), probably due to the effect of D-galactosamine on intracellular ATP levels.