The technique of pulsed electron-beam high-pressure mass spectrometry was used to investigate the sequential cationic chemistry in humid air streams at 4.2 x 10(2) Pa and 380 K. The system was then modeled using the ACUCHEM program, incorporating thirty-five reactions taken from the formulations given in Part I of the new National Institute of Standards and Technology (NIST) Chemical Kinetics Database for Humid Air Plasmas. The resulting temporal ion profiles were found to be in qualitative agreement with the laboratory data. Analogous pulsed elect,on-beam measurements were also carried out with humid ab samples containing low levels of toluene, and these results were also reproduced qualitatively by a model incorporating forty-eight reactions after the inclusion of an unexpected, but crucial, channel involving the reaction of an intermediate air-generated cluster ion with toluene. The benefits of laboratory validation of predictive databases in systems for which the literature data are incomplete are emphasized.