In the present paper we have evaluated IgD serum levels of 84 randomly selected HLA-typed healthy Sicilians. The values were analysed according to age, sex and HLA-DR phenotypes. No correlation between age and IgD serum levels was found in our population since all subjects were in a narrow age range. Furthermore, no significant association was found between IgD serum levels and gender of studied subjects. The evaluation of IgD serum levels according to HLA-DR phenotypes revealed that HLA-DR1 positive subjects displayed significantly higher values. These results are in agreement with previous reports showing that HLA phenotypes may be involved in the control of serum immunoglobulin levels. Furthermore, present data strengthen our suggestion that HLA-DR1 phenotype is related to the 'high responder' immunological profile.