The responsiveness of eccrine sweat glands to intradermally injected carbachol was studied in six male and six female healthy volunteers and six male and six female patients suffering from anxiety neurosis. Consistently greater responses to carbachol were obtained in the healthy males than in the healthy females. Analysis of the dose-response curves showed that this was reflected in a higher value of Emax in the males. Consistently greater responses to carbachol were obtained in the anxious males than in the healthy males, this being reflected in a higher value of Emax for the anxious subjects. Consistently greater responses to carbachol were obtained in the anxious females than in the healthy females, this being reflected in a higher value of Emax for the anxious subjects. In contrast to the results obtained with the healthy subjects, there was no sex-related difference in responsiveness to carbachol among the anxious patients. It is suggested that the hyper-responsiveness of sweat glands in anxiety states involves the sensitization of normally 'dormant' sweat glands by impulse flow in sudomotor sympathetic fibres. The upper limit to the value of Emax for carbachol, which may be determined by the number of potentially responsive glands, may be similar in the two sexes.