The GEM 4S device, a sexuo-diagnostic plethysmograph, provides continuous recording of changes in the volume of human genitalia. Moreover, it provides galvanic measurement of skin response, which evaluates the psychological and emotional status of the person measured. Data measured are transmitted on-line to the PC, where they are displayed and recorded by the user's software. This software provides records of stimuli displayed to the person measured and also contains a patient database with basic personal information and data measured. It is designed as a compact portable device placed close to the patient and is powered by batteries. Communication with the PC is wireless.