Immunoglobulin E (IgE) was measured in the sera of 18 healthy adult volunteer donors, 67 adults with various types of solid neoplasms, and 17 adults with clinical allergy by means of a double-antibody radioimmunoassay. There was no siginificant difference in the geometric mean serum IgE level between all cancer subjects and the healthy control subjects except that cancer and noncancer patients who had definite clinical allergies showed an increased mean IgE level. Similarly, there was no significant difference in the mean IgE level of any of the six cancer subgroups studied when compared to the control mean. Thus, there was no evidence reflected in serum levels that IgE plays a role in the immunopathology of the cancer population tested.