A slightly modified version of provisional research criteria for so-called 'schizo-affective and related psychosis', as recently published by the St. Louis Group, was used to investigate the case records of 116 Schneider-oriented first admissions of schizophrenics without first rank symptoms (Schneider-negative) who were hospitalized in a German center during the years 1962-1971. The sample contained 19.8% (23 cases) of research diagnosable schizo-affective illness as thus defined. 'Full' affective research criteria were satisfied by 13 of these schizo-affectives, and 10 were able to fulfill the 'adjusted' affective criteria assumed to be indicative of labile mixed mood states. The sample was then further analyzed in terms of 'schizophreniform' psychoses and 'atypical schizophrenia'. The findings seem to support the view that a non-negligible segment (23.3%) of Schneider-negative schizophrenia actually may represent either research diagnosable schizo-affective or affective disorders or satisfy criteria for both diagnoses.