We compared the provocative concentration (PC) values obtained by two different methods of performing bronchial histamine challenge. One test was done on an APTA, an apparatus which allows simultaneous provocation with histamine and measurement of airway resistance (Rtot) by the interrupter method. The second test was a conventional tidal breathing method, with measurement of the FEV1. There was a high correlation between the PC20-FEV1 and the PC30-, PC40- and PC50-Rtot values. The correlation coefficients were 0.85, 0.71 and 0.70 (P less than 0.05) respectively. We further tested the reproducibility of the histamine challenge done on the APTA. When the PC30-Rtot values were compared, a correlation coefficient of 0.56 (NS) was found. For the PC40- and PC50-Rtot values the correlation coefficients were 0.65 (P less than 0.05) and 0.70 (P less than 0.02) respectively. We conclude that the APTA is useful for routine bronchial histamine challenge when 40-50% increase in basal Rtot is used as endpoint.