Pastures were topdressed with pellets of 10% Mocap at a rate equivalent to 2.13 kg active ingredient (a.i.j zha. Two groups of lactating dairy cows were withheld from grazing the treated pasture for 7 and 14 days respectively. After exposure to the treated pasture none of the animals developed symptoms of organophosphate poisoning at any time, and their blood cholinesterase activities were not affected. Mocap was not detected in milk samples taken at intervals of 8 hours, and 1, 3, 7, and 14 days after they had been put on topdressed pasture (i.e., all samples contained less than 0.010 ppm Mocap on a butterfat basis). Milk yields were not affected by the treatment.In two other trials, a 4 ha paddock on each of two commercial dairy farms was topdressed with 10% Mocap pellets at a rate equivalent to approximately 2.24 kg a.i.rha. The milking herd on each farm was allowed to graze the treated pasture from 14 days after topdressing. Samples representative of milk from the whole herd were taken 12 hours, and 3 and 7 days after exposure to topdressed pasture. The l2-hour sample from one farm contained 0.014 ppm Mocap on a butterfat basis, but all other samples contained less than 0.010 ppm Mocap. There were no symptoms of organophosphate poisoning or effects on milk yields or milk flavour.