To determine middle ear pressure (MEP) changes during natural rhinovirus colds, adults with illness for < or = 3 days were tested by digital tympanometer daily for 5 days (study 1) or every other day for 7 days (study 2). Abnormal MEPs (< -50 or > +20 mm H2O) were found in 72% of 36 patients in study 1 (P < .001, vs. baseline of 11%) and 76% of 55 patients in study 2 (P < .001, vs. 15% of 103 healthy controls). Major abnormalities (> or = +100 or < or = -100 mm H2O) were found in 61% of patients in study 1 (P < .001, vs. baseline of 0) and 47% in study 2 (P < .001, vs. control of 5%). MEP abnormalities usually resolved by day 14. Only 1 subject developed clinically apparent otitis media. Earache or respiratory symptom scores did not correlate with MEP abnormalities. These results indicate that natural rhinovirus colds in adults are frequently associated with marked but transient MEP abnormalities.