It was hypothesized that females would respire more rapidly than males and that deceptive examinees would have a higher proportion of slow breathers than nondeceptive examinees in their efforts to defeat the polygraph. The study randomly selected a sample of cases from the confirmed case database of the Department of Defense Polygraph Institute. The sample consisted of 234 first-session criminal polygraph examinations. All examinations were conducted according to the Zone Comparison Technique protocol. The cases were collected during a 100-percent review of all criminal polygraph cases conducted by the U.S. Army Criminal Investigations Division over a 26-month period, beginning on January 1, 1995. Average breathing rates were different for females and males, as expected; however, the finding that tonic respiration rates for deceptive and nondeceptive examinees were not significantly different was unexpected. The data indicated that the behavior of slow breathing was not unique to either deceivers or truthtellers. What was apparently meaningful, however, were the very large changes in tonic respiration rates between charts. Because respiration is subject to voluntary control, this pattern is more likely a manifestation of a conscious behavior, not a psychophysiological response. Examiners should pay attention to examinees who significantly alter the speed of their respiration from chart to chart, especially when the change exceeds 20 percent between any two charts. 3 tables and 2 references