Primary health care (PHC) in developing countries continues to rely heavily on paramedical personnel. Using a structured questionnaire, 207 PHC workers in Nigeria were assessed on the concept, attitude to, detection and treatment of mental disorders. PHC workers without previous exposure to mental health training were significantly more likely to hold on to traditional views on the aetiology of mental disorders. Most of the health workers (82%) indicated that mental disorders accounted for 5% or less of their patient load. Detection rate for the vignette on neurosis as a case of mental disorder was poorer than that for psychosis (36% vs. 71% of respondents respectively). Psychopharmacological knowledge of the PHC workers was found to be poorest for antidepressant medication. Only 30% of the health workers could suggest specific types of mental health programme that could be introduced at PHC level. Many of them (72%) expressed a generally negative attitude towards mentally ill patients. Suggestions are made on the short and long term training requirements of the PHC workers in order to ensure the successful integration of mental health care into the primary health care programme in Nigeria.