We analyzed a large multiplex schizophrenia pedigree collected in mid-eastern Japan using 322 microsatellite markers distributed throughout the whole autosome. Under an autosomaldominant inheritance model, the highest pairwise LOD score (LOD = 1.69) was found at 4q (D4S2431: theta= 0.0), and LOD scores at two other loci 3q (ATA34GO6) and 8q (D8S1128) were 1.62 and 1.46, respectively. In multipoint analysis, LOD scores of the regions on 4q and 3q remained at a similar level; however, the LOD score of the region on 8q apparently decreased. Additional dense map analysis revealed haplotypes on 4q and 3q regions shared by affected individuals. On chromosome 4q, the haplotype spanning about 8 centiMorgans (cM) was shared by four of six genotyped individuals with schizophrenia and one affected individual whose haplotype was estimated. On 3q, the haplotype spanning about 20 cM was shared by five genotyped individuals with schizophrenia. We obtained two candidate regions of major susceptibility loci for schizophrenia on chromosomes 3q and 4q. (c) 2007 Wiley-Liss, Inc.