Sixty-one subjects were exposed in a climate chamber for 5.5 hours to a controlled atmospheric
environment. Formaldehyde vapours were added in concentrations of 0, 0.15, 0.40, or 1.20 mg/m ~.
The exposures were arranged in a 4 x 4, balanced latin square design, involving four days in each
of four weeks. The subjects were all males. Of these, 32 had occupational exposure to formaldehyde
in industrial productions for more than five years. Twenty-nine were randomly selected,
matched controls from the normal population. The hypothesis tested was that significant, but
different dose-response relations exist in a number of performance tests for these two groups of
subjects. The results indicate such differences in reactions to tests of short term memory and
ability to concentrate (digit span tests, digit symbol test, graphic continuous performance test)
and an addition test. Whether these results indicate chronic or acute CNS effects or they are
caused by distractive sensory irritation due to formaldehyde exposure is discussed.