Depiction of strategy for amplification of GSTT1, β-globin, and GSTM1 genes (left) with resultant ethidium bromide–stained electrophoresed products from representative patient samples. The numbers 1 through 8 correspond to individual patients, with positive GSTT1, β-globin, and GSTM1 alleles yielding 480-, 268-, and 219-bp fragments, respectively; eg, patients 1, 5, and 7 are null for GSTM1, patients 2, 4, and 8 are null for neither GSTM1 nor GSTT1, patient 3 is null for GSTT1 only, and patient 6 is null for both GSTM1 and GSTT1. Absence of the PCR product indicates the null genotype. The far left lane (M) indicates the molecular-weight marker.