Phase I of this study demonstrated the feasibility of measuring the efficiency and capacity of sorbents in tube samplers for contaminant gases. This was accomplished by measuring concentration at various points along the length of the diffusion path during sampling by removing small aliquots with gas-tight syringes and injecting them into a gas chromatograph. With hexane as the gas and activated charcoal as the sorbent, the procedure was successful. Phase II involved application of the principle to gases of importance in diesel exhaust using a variety of sorbents. High concentrations of the test gas clearly demonstrated the differences in both efficiency and capacity of the sorbent for each of several gases. The chief drawbacks of the system were that efforts to determine more toxic gases at realistic occupational exposure levels or to determine formaldehyde at any level using the flame ionization detector were unsuccessful. It was concluded that, although the method is feasible, ore-sensitive methods of measuring concentrations of gas in the tube must be developed to make the procedure applicable to regions of chief industrial hygiene interest.