Characteristics of diffusive samplers with sorbent strips aligned longitudinally along the sampler were investigated mathematically. For purposes of analysis, it was assumed that external concentration of the chemical of interest varied slowly enough that transients in sampler air spaces had negligible effect on estimates of the time weighted average concentration. Equations were developed to calculate the mass sampling rate in terms of the analyte diffusion constant, the sampler cross sectional area, and the external concentration. Means of estimating the time weighted average of the external concentration in terms of the sample mass regardless of the time dependence of the concentration were also developed. Modifications of this relationship were developed for samplers which employed a semipermeable entrance membrane. Concentration distribution and analyte streamlines were determined for a specific, idealized sampler geometry. On the basis of these calculations, it was determined that a one to one correspondence existed between the stain length and exposure to the hazardous gas or vapor under investigation regardless of changes in the concentration over time. The changing sampling rate during exposure did not induce inaccuracy in time weighted averages of the concentration. Consequences of the three dimensionality of the flow of analyte from sampler entrance to sorbent strip manifested themselves only subtly, often being negligible. The author concludes that, in spite of remaining uncertainties regarding sampler performance, the direct reading diffusive longitudinal strip monitor may prove a useful tool in the field of industrial hygiene.