The plasma membrane of Paramecium tetraurelia comprises two morphologically distinct components; a membrane that encloses the cell body and a ciliary membrane. In order to investigate the relative contributions of the two membranes to attractant-induced membrane potential changes, cells were deciliated with ethanol and their subsequent responses to attractants examined. Deciliation did not significantly affect the magnitude of the hyperpolarizations evoked by acetic or lactic acids, and had no effect on the concentration dependence of responses to folic acid. We conclude that the components necessary for detection and response to attractants are not exclusive to the ciliary membrane of P. tetraurelia. Deciliation of Paramecium concomitantly permits localized chemical stimuli to be applied directly to the cell surface in the absence of strong fluid currents that are generated by the activity of the locomotory organelles. By systematically applying K2 folate to a number of sites on the cell surface, it has been possible to demonstrate an anterior-posterior gradient of chemosensitivity on the cell body of P. tetraurelia.