Knowledge of specific IgE bound on immunosorbent as assayed by RAST is useful but cannot give a complete description of the biological states of patients concerning IgE antibodies. Using a computer program based on a least squares error method and knowing the amount of bound specific IgE antibodies to grass pollen antigens in a serum at each of the four tested dilutions it is possible to calculate the absolute value of specific IgE antibody level, the relative value of affinity constant and the relative proportion of IgE antibodies to the total amount of specific (IgE plus non-IgE) antibodies. It is found that specific IgE antibodies account for high percentages of the total IgE protein (mean of 20%). High differences in affinity constant and in the proportion of IgE antibodies to the total amount of antibodies could be found between sera. Severity of grass pollen allergy could be related to the absolute level of IgE antibody, but no definite conclusion could be made on the importance of affinity constant and the proportion of IgE antibodies to the total amount of antibodies.