Immunoglobulins and complement were quantitated in 100 healthy adult Omanis in order to establish a reference range based on local data. Mean values were IgA 2.38 g/L, IgM 1.14 g/L, IgE 241 kiu/L, C3 7.44 micro mol/L and C4 1.57 micro mol/L, values similar to those found in the West. However, the mean level of IgG was almost 50% higher than that found in North America and Europe, that is, 14.63 g/L compared with 10-11 g/L. The values for IgG, IgA, IgM and IgE are similar to those reported for Iraq, but IgG levels were much lower than those found in Iran (25.52 g/L), although IgA, IgM and IgE were comparable. Comparison of Omani data with that for Saudi Arabia showed significantly more IgG in Oman (14.63 versus 11.68 g/L) and significantly less IgM (1.14 versus 1.66 g/L). IgA and IgE levels were similar. As reported elsewhere, females had significantly more IgM than males (1.32 versus 0.97 g/L). The levels of IgG subclasses in Oman are 9.44, 4.01, 1.06 and 0.62 g/L for IgG1-4 respectively. The percentage of the various subclasses are very similar to those reported elsewhere, that is, 62%, 27%, 7% and 4% for IgG1-4. However, in Iraq, a higher percentage (and level) of IgG3 (16%) and the lower IgG2 (18%) compared to Oman may reflect differing immune responses resulting from exposure to different microorganisms. It is essential to use local reference data when evaluating patients.