Exposure to carbonless copy forms has been associated with subjective reports of respiratory and skin irritation, but objective measurements of human reactions to exposure are lacking. Thirty workers with complaints of prior sensitivity to the forms were given brief, controlled exposure to vapors from carbonless forms and from bond paper in random, single-blind fashion. Nasal impedance increased 34% after exposure to carbonless forms (P < .025) and rose 8% after exposure to plain paper (P > .10). However, frequency of symptoms did not differ between the two exposure modes, and was not correlated with the nasal measurements. Quantitation of nasal congestion by this technique may be a sensitive measure of short-term reaction to inhalation of irritants.