The largest cluster of positive results, considering both bipolar and schizophrenia, occurs in the 4p region that includes D4S394 and DRD5. Four groups report at least weakly positive linkage analyses this region for bipolar disorder, and two groups find weak positive allelic association with schizophrenia in the region, although at separate markers. On the other hand, at least five groups do not find evidence for linkage of bipolar disorder to this area of 4p. The pattern on 4q is less clear, with a mixture of negative and small positive results in either bipolar or schizophrenia families. Additional allelic association and TDT studies of 4p markers in bipolar disorder and in schizophrenia might be able to narrow the focus of the 4p investigations. The dopamine D5 receptor gene has seductive qualities as a candidate gene because of the pharmacology of psychotic disorders. It would be helpful to have additional markers developed close to or in the recoding region of DRD5 in order to have the extra information at the DNA level provided by haplotype analysis. Chromosome 4 susceptibility loci may figure prominently in alcoholism, although a great deal of work remains to be done. With just two groups reporting here, only a limited assessment of the overall effect of the ADH cluster and the GABA cluster is possible. However, these loci have merit as candidate genes, and thus further work on the current and additional families is clearly indicated.