Recent years have witnessed numerous attempts at identifying the biological correlates of impending psychosis. Biochemical markers may theoretically provide a powerful approach to identify at-risk individuals, potentially leading to more effective intervention strategies to treat them. Hopefully, future developments in the field of research biochemistry in patients with at risk mental states or prodromal symptoms will make this approach ideal for screening and monitoring purposes. In this review, we provide an overview of the different biochemical markers which have been recently demonstrated to be altered in the biological fluids of patients with impending psychosis. We will also examine the practical issues that seem to be limiting the effective integration of biomarkers into clinical development.