To assess respiratory rate as an indicator of acute respiratory dysfunction, we studied 58 consecutive patients four times daily during the postoperative period. Of 825 measurements of respiratory rate, 726 (89%) were normal (24/min or less). Elevations in respiratory rate without respiratory dysfunction were found in only 4% of all measurements. Patients without lung disease had a mean respiratory rate of 18 +/- 4/min, while patients with an abnormal respiratory rate and respiratory dysfunction had a mean of 27 +/- 5/min. Our study demonstrates that respiratory rate, if carefully measured, is a sensitive and reasonably specific marker of acute respiratory dysfunction.