Using an in-vitro test, the presence of formaldehyde-specific IgE antibodies was investigated in sera from four groups of individuals exposed to formaldehyde by different routes and concentrations. Group (A) 28 subjects living or working in rooms or places where formaldehyde-containing construction materials were used: (B) 18 subjects occupationally exposed to relatively high concentrations of formaldehyde; (C) 12 paramedic employees working in a renal dialysis unit where formaldehyde-sterilized dialysers were being used; and (D) 28 subjects undergoing haemodialysis with these formatdehyde-sterilized dialysers. Formaldehyde-specific IgE antibodies could be detected in only one of the 86 serum samples. This particular sample was from a worker occupationally exposed to formaldehyde (group (B)), but who did not show any work-related symptoms. In two pools of control sera from unexposed subjects no specific IgE antibodies to formaldehyde were detected. It is concluded that exposure to formaldehyde, even in relatively high concentrations, rarely evokes the production of specific IgE antibodies. The presence of these specific antibodies is not necessarily attended by allergic symptoms. On the other hand, the symptoms supposed to be related to formaldehyde exposure and reported in this study by 24 out of 28 subjects in group (A), and some of the subjects in groups (B) and (C), cannot be attributed to an IgE-mediated sensitization to formaldehyde.