Opiates are known to induce immunosuppression in their users (addicts). Evidences supporting their role in suppressing a variety of immunological end points in addicts have been reported by several investigators. In the present study, we investigated the changes in serum immunoglobulin (Ig) levels and their correlation with Mu opiate receptor (MOR) genotypes. Eighty-seven users and forty-five non-users were recruited for the study. Genomic DNA, isolated from the peripheral blood, was used for genotyping for C17T and A118G polymorphism using PCR-RFLP method. The frequency of A and G alleles in non-users was 89% and 11% respectively, whereas in addicts, it was 67% and 33% respectively. Case control analysis between groups revealed that 118G allele was associated with opioid dependence [Chi square (chi2) = 13.56, odds ratio (OR) = 3.90, confidence interval 95% (CI 95%) = 1.80-8.67, p = 0.000231]. C17T polymorphism showed no association with opioid dependence [(chi2) = 0.9, OR = 2.49, CI 95% = 0.528-16.12, p = 0.343]. Mean Ig levels, both IgG (student's t-test = 2.2738, p = 0.007) and IgA (student's t-test = 2.848, p = 0.0051) differed between opiate users and nonusers. IgG and IgA levels were also significantly different in individuals with different MOR genotypes. Immunosuppression was observed in AA genotype-bearing individuals, while no suppression was seen in AG and GG genotypes bearing individuals. In case of C17T polymorphism, both CC and CT genotypes bearing individuals showed immunosuppression, as judged by circulating Ig levels.