Forty-one patients admitted into single-bedded isolation cubicles in an infectious diseases unit were assessed for evidence of mental disturbance. By use of the Crown-Crisp Experimental Index as a measure of mental state, the scores for somatic anxiety, free floating anxiety, and the total score were found to be significantly raised on admission, falling towards those found in a control general practice population by the time of discharge from hospital. Higher scores were associated with a past history of mental illness. There was, however, no statistical correlation between the psychological indices and consumption of alcohol, smoking, or patient's sex. Clinically apparent behavioural disturbance, mainly anxiety and agitation, was seen in 12 patients. Overall, patients expressed a preference for single rooms and did not find the isolation rituals disconcerting. The findings indicate that anxiety in patients with acute infections is more related to their illness and referral to hospital than to their imposed isolation. Only those patients with a past psychiatric history are likely to benefit from transfer to an open ward during convalescence.