These authors studied porphobilinogen excretions and subjective psychological data in relatives of patients with porphyria, a nonsex-linked hereditary metabolic defect. Porphobilinogen excretion and subjective distress reactions correlate well with each other and with the emotional stress caused by illness in a relative who is acutely ill with a disease to which the subjects themselves may also be prone. The authors do not suggest a psychogenic causality as such, but adduce data to show that a pre-existent metabolic defect may be raised to clinical levels by psychic stress.