AbstractToxic and immunotoxic effects of p-chloroaniline-a metabolite of herbicide monolinuron-were investigated in peripheral blood leucocytic suspensions of five sheep using a migration-inhibition test. The toxic effect of p-chloroaniline was recorded at concentrations 1.0 to 0.1 mg.ml−1and the immunotoxic one at concentrations 0.01-0.001 mg.l−1. The toxic effect was demonstrated by total inhibition of leucocyte migration. The immunotoxic effect, determined as mitogenic activation of leucocytes by phytohemagglutinine, concavaline A and lipopolysaccharide, was detected at 10 to 100-fold lower concentrations of p-chloroaniline than those which resulted in toxic effects.