Studies on changes in breathing patterns of rats due to exposure to acrolein and the Leflon pyrolysis product perfluorisobutylene (PFIB) were performed to evaluate a new developed integrated system of nose- only exposure and multiple monitoring of breathing of up to eight rats. Measurements of breathing was based on nose flow pneumotachography using differential pressure transducers and monitoring on the videoscreen the 12-s breathing records of 4 rats, including online analysis of respiration frequency (f) and respiratory minute volume (V̇(t) simultaneously. Acrolein concentrations (7- 54 ppm) caused an immediate change of the breathing pattern in exposed rats characterized by a concentration-dependent decrease of f and a similar change of V̇(t). Analysis of the breathing records showed increasing postinspiratory apneic periods as major cause of the decreased f. An RD50 of 4.6 ppm for acrolein was calculated (95% confidence limits 2.4 and 7.2 ppm). Acute nose-only exposure of rats to 100 ppm PFIB during 6-18 min did not change the breathing pattern immediately. However, 24 h after exposure a changed breathing pattern was monitored, characterized by small preinspiratory apneic pauses, lung edema was confirmed at histopathological examination. Continued monitoring of breathing patterns after the acute exposure of PFIB showed normal breathing patterns in recovering rats.