A rating scale consisting of 15 behaviour variables has been constructed in order to obtain a quantification of the clinical signs and L. E. Jönsson and K. Sjöström, Psychiatric Research Center, University of Uppsala, Ulleraker Hospital, symptoms in amphetamine psychosis. Fifteen cases of amphetamine psychosis in intravenous abusers have been observed and rated every fourth hour for at least ten days. A high degree of agreement between the raters was obtained for each variable. It was shown that 'lack of concentration', `delusions of persecution', `increased motor activity', `disorganization of thoughts', `lack of insight', `hallucinatory behaviour', `anxiety and fear' and `suspiciousness' measured frequently occurring symptoms during the first two days. There were indications of an overlapping between some variables.