A population of 228 healthy elderly subjects was studied for immunoglobulin levels, titers of antibacterial antibodies and the prevalence of auto-antibodies, to determine the possible associations between these humoral parameters and age. Serum levels of IgG and especially IgA and the incidence of auto-antibodies (antinuclear antibody and rheumatoid factor) were increased in aged subjects. Some differences were found between males and females. The levels of IgA and natural antibodies were significantly higher in males: the changes of prevalence of auto-antibodies with age were different in males and females; furthermore the correlation between the level of IgG and that of natural antibodies was significant in males. There was a slight positive relationship between the prevalence of auto-antibodies and the level of natural antibodies.