This paper reviews restraints on the provision of mental health services in primary health care under the broad categories of physician profile, patient behavior, the nature of psychiatric illness as presented in primary care, and service system characteristics. An extensive research agenda is proposed toward improving mental health care in primary care settings. Research recommendations focus on the following types of issues: seeking a better understanding of the clinical decision making process when confronted with psychological or emotional problems, designing more focused mental health training for primary care physicians and nurses, providing patient education to encourage communication of psychosocial problems to medical providers, clarifying the nature and course of psychiatric disorder in primary care, designing innovative clinical interventions applicable to primary care, and examining organizational models for better coordination of health and mental health services.