Eight family outbreaks of clinical or subclinical psittacosis in Israel after exposure to infected birds were studied. Throat cultures for Chlamydia psittaci and serological tests for Chlamydia species, including strain TWAR, were obtained from 37 people. Cloacal smears and cultures of internal organs for C psittaci were taken from 9 dead birds. 62% of the people studied had symptoms, and 67% of the birds that died had previously been sick. Evidence for acute C psittaci infection was found in 81% of patients (30/37). Diagnosis was established in 22 by isolation of the causal organism from throat cultures and in 8 by positive IgM serology (reciprocal titre greater than or equal to 8) with evidence of acute seroconversion or clinical findings compatible with the disease, or both. No serological evidence for acute TWAR infection was found. All birds studied had microbiological evidence of C psittaci infection, and most had abnormal findings on necropsy.