Serum levels of the immunoglobulins: IgG, IgA and IgM were determined by the single radial immunodiffusion technique of Mancini in a total of 122 apparently healthy subjects consisting of 43 children (20 males; 23 females) aged 5-12 years and 79 adults (39 males; 40 females) aged 18-65 years resident in Port Harcourt, southeastern Nigeria. The effects of age and sex on the serum levels of the various immunoglobulin types were also determined. The mean values and ranges for the various immunoglobulin types are presented for both children and adults. Although, female children were found to have significantly lower mean values of IgA compared to male children (p<0.05), there were no significant differences in the mean values of both IgG and IgM between male and female children involved in the present study (p>0.05). However, female adults had significantly higher mean values of IgG and significantly lower mean values of IgA compared to male adults (p<0.05); suggesting a significant gender difference in the value of both IgG and IgA amongst adult subjects. No significant differences were observed in the mean values of any of the various types of immunoglobulin between adults and children. The present study reports mean values of the various types of immunoglobulin in apparently healthy children and adults resident in Port Harcourt, southeastern Nigeria. Significant gender differences were observed for some of the immunoglobulin types only amongst adults. Our results suggest that these gender differences amongst adults were apparently a gradual build-up from childhood. The results also confirm suggestions that levels of some immunoglobulin types seen amongst African adults may have possibly been attained during childhood. Our study could be of value since previous reports in this regard have been relatively scanty especially in this part of Nigeria.