Schizophrenic patients were recruited into a trial of a prophylactic behavioural intervention with families. Families with at least one high Expressed Emotion (EE) relative were randomly allocated to one of four intervention groups: Behavioural Intervention Enactive; Behavioural Intervention Symbolic; Education Only; Routine Treatment. Patients from low-EE families were randomly allocated to two groups: Education Only or Routine Treatment. Relapse rates over nine months after discharge were significantly lower for patients in the two Behavioural Intervention, compared with Education Only and Routine Treatment groups. There was little difference between the two low-EE groups. Patients returning to high-EE relatives showed significantly higher relapse rates than those returning to low-EE relatives, in groups not receiving active intervention. Changes from high to low EE occurred in the Behavioural Intervention groups, and similar although less extensive changes occurred in the Education Only and Routine Treatment groups. Changes in criticism and marked emotional over-involvement (EOI) occurred generally in high-EE groups but were larger in magnitude in the Enactive and Symbolic groups. Reduction of hostility only occurred in the Behavioural Intervention groups. These results give partial support for the causal role of EE in relapse. There were no significant differences between the groups with respect to contact with the psychiatric services or medication.