Phenotype and gene frequencies of 24 blood group, serum protein and red cell enzyme loci are examined in four endogamous groups (Brahmin, Maratha, Gujarati Hindu Patel and Parsee) of Maharashtra, Western India. Several genetic systems are investigated for the first time in this region. Genetic heterogeneity is suggested, although the overall variation shows general agreement with the populations already studied from Western India. In addition to the historical migration and possible selective effects, the present-day gene pool of Maharashtra is greatly influenced by sociocultural adaptation and breeding structure. The presence of rare alleles ESD*5, and BF*S1 suggests a Caucasoid affiliation of populations of this region.