In spite of advances in neuroleptic treatment, relapse of positive symptoms continues to punctuate the course of schizophrenia. In this paper the conceptual and empirical basis for early intervention in the process of psychotic relapse as a preventative manoeuvre is evaluated. The predictive efficacy of early, 'prodromal' signs, their nature, and the utility of early detection and intervention strategies are reviewed. There is strong evidence that relapse is preceded by early signs, but the classical (medical) concept of prodrome is inadequate to explain the findings. The early detection and treatment of early signs appears to confer protection from relapse, but the active ingredients of the pharmacological and psychological based treatment studies are as yet unclear and suggest important avenues for future research.