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The role of socio-cultural differences on the effects of inbreeding on mortality was examined in 1126 families of representative populations of two scheduled castes (Madiga and Mala) two forward castes (Reddy and Vysya) and Maheshwaris a noninbred urban community. The effects of inbreeding (F) on mortality were estimated using the exponential model: 1 — L = exp [— (A + BF)].The estimates of the random load ‘A’ were higher in low caste groups than in high castes, whereas the estimates of the inbred load B, were found to be negative in low castes (Mala = — 0.34, Madiga = — 1.14) but positive and significant in the high castes (Reddy = 1.87, rural Vysya = 2.37, urban Vysya = 3.40). It is suggested that negative regressions in the low caste groups might have been due to low genetic mortality resulting from a lower frequency of deleterious genes and higher homozygosity of genes adapted to the environment under the high levels of inbreeding in these groups.