Summary The adequacy of sexual functioning in the male depends on a complex interaction between psychological, hormonal and neurophysiological factors. Disturbance of any one of these factors may lead to sexual inadequacy. In the majority of cases no gross abnormality is found but the absence of gross hormonal or neurophysiological abnormality does not necessarily imply a purely psychological cause. Individual variations in the pattern of response of the autonomic nervous system or in the ability to learn control of autonomic responses such as erection or ejaculation may be sufficient to account for some cases of inadequacy and in others may increase the susceptibility to psychological factors. Further research is required to clarify these undoubtedly important psychophysiological relationships. Treatment has been most successful when it has taken into account both psychological and physiological factors. The advances made by Masters & Johnson (1970) in this area have partly depended on their earlier physiological and anatomical studies of sexual response (Masters & Johnson, 1966). It may be that in some cases the use of anxiety-reducing drugs or androgens will be all that is required but further work is required to identify such cases. The placebo effects of such preparations should not be overlooked particularly as many cases of sexual inadequacy are based on lack of confidence or ignorance and require little more than good advice or reassurance. Considerable advances in our understanding of these problems have been made in the past 20 years and techniques of endocrine, physiological and behavioural assessment are now available which should enable further progress to be made in the near future.