The underlying mathematical model of the forcing sinewave alveolar amplitude response technique (AART) for measuring lung volume and perfusion is investigated. Making use of numerical techniques, we are able to to evaluate the effects of several assumptions which are implicit in the original technique introduced by Zwart et al., J. Appl. Physiol. 41: 419-429, 1976, and development by several other workers. In particular we are able to show that AART is appropriate for gases of a wider range of solubilities than originally suggested, allowing it to be used with agents, such as nitrous oxide, which are more clinically acceptable. In addition, we are able to show that the effects of recirculation times are likely to be very small using figures for standard man. A least squares parameter recovery technique proves to be very robust to simulated measurement errors and is used to quantify the effects of the modelling assumptions.