Sick-building syndrome symptoms associated with indoor air volatile organic compounds, including formaldehyde in new or newly remodeled houses, have been increasingly highlighted, and are known as "sick house syndrome" in Japan. We developed a competition enzyme-linked immunosorbent assay for measuring formaldehyde in serum. The specificity of the antiserum generated with formaldehyde-rabbit serum albumin conjugates and the application to the detection of formaldehyde in serum were evaluated. The antiserum selectively reacted with formaldehyde conjugated to rabbit, human, rat and bovine-serum albumins, but not with unconjugated albumins. The quantitative working range of formaldehyde-human serum albumin conjugates was from 0.5 to 500 ng/well.