Dr Mehra has made significant contribution in the subject of 'histocompatibility and immunogenetics' and has identified the role of HLA-linked genes in the important diseases of India. He has shown that susceptibility to leprosy and tuberculosis is associated with a subtype of HLA-DR2 carried on a unique class II haplotype. He has further Shown that Indian patients show a pattern of DR and DQ association in rheumatoid arthritis and insulin dependent diabetes mellitus quite distinct from that of the Western Caucasian patients.