Choline uptake and incorporation into Schistosoma mansoni is used as a model for investigating transport across and formation of a double bilayer surface of a syncytial transporting epithelium. Choline uptake reached a maximal rate during the first 2 min (Vmax = 0.27 mumol mg-1 protein min-1; Km = 36 microM). Choline uptake during a 30 min incubation was similar to that of single bilayer transport systems described in the literature. Choline incorporation into phosphatidylcholine was saturated above 40 microM external choline concentration (Vmax = 3.7 pmol mg-1 protein min-1; Km = 7 microM). The low rate of choline efflux and the half life of the tissue choline pool (T 1/2 = 3 h), suggests that free choline pools available for efflux in S. mansoni are small. This model allows the determination of whether a proposed effector of membrane phosphatidylcholine synthesis and turnover alters surface bilayer formation through changes in transport of the precursor across the apical surface.