A case of prolonged action of suxamethonium in a patient with gestational trophoblastic disease is reported. Postoperatively the patient was found to have markedly reduced plasma cholinesterase activity (363 IU/litre) with a normal cholinesterase phenotype. Consequently plasma cholinesterase activity and phenotype were measured in six other patients with the condition and these results compared with those of 22 patients with normal first trimester pregnancies undergoing therapeutic abortion. Plasma cholinesterase phenotype was normal in all patients studied. The activity was significantly decreased (p less than 0.05) from the normal range (620-1370 IU/litre) in all patients with trophoblastic disease. In the 22 patients with normal pregnancies, 14 had activity values in the abnormal range (less than 620 IU/litre) while the mean cholinesterase activity of the group as a whole was significantly decreased (561.8 IU/litre, p less than 0.05) below the normal range. These results confirm the presence of a decrease in plasma cholinesterase activity in early pregnancy and provide new evidence for a decrease in activity in a pseudopregnancy state.