We estimated the frequencies of GSTM1 and GSTT1 "null" homozygotes in 10 di
fferent ethnic populations of India by a genotyping method based on polymer
ase chain reaction. These populations, inhabiting diverse geographical loca
tions and occupying various positions in the sociocultural hierarchy, were
represented by a sample of 299 unrelated individuals. Frequencies of GSTM1
and GSTT1 "null" homozygotes varied from 20% to 79% and 3% to 39%, respecti
vely, across the study populations. Maximum frequencies of GSTM1 and GSTT1
"null" homozygotes (79% and 39%, respectively) have been observed in the sa
me population (Jamatia). Frequencies of homozygous "null" genotypes at the
GSTM1 and GSTT1 loci show a significant positive correlation in these popul
ations, which is contrary to expectations. A possible implication is that t
he two enzymes are working in tandem, instead of working in a complementary
way.