Total serum IgE was determined with the PRIST technique, and specific reaginic antibodies against 10 allergens were measured in 163 healthy adults with no personal or family history of symptoms indicative of atopy (Group A). 103 non-atopic adults with a family history of atopic diseases were similarly investigated (Group B). When all subjects who at the second interview presented with a history of atopic symptoms and those with positive RAST results were excluded, the geometric mean serum IgE value for Group A was 14.5 (SD = 2) - 94.4 U/ml and for Group B 14.4 (SD = 2) - 130.2 U/ml. There was no significant difference in the IgE values between men and women. Subjects under 40 years of age had significantly higher IgE values than subjects over 40 years. In the series of 276 dermatitis patients the geometric mean IgE value for the men was significantly higher (46.8) than for the women (28.8 U/ml). There was a highly significant difference in the mean serum IgE levels between the patients with a personal history of atopic diseases and the other patients. Patients with present atopic disease had significantly higher mean IgE values than those with past atopic disease while no significant difference was discernible in the mean IgE levels between the non-atopic patients from atopic families and those with no personal and family atopy. Three years later, total serum IgE was controlled in subjects with initial IgE levels greater than 100 U/ml. During this time, eight subjects had developed an atopic disease. In most cases, there were only slight variations in the IgE values.