A sheet membrane inlet mass spectrometric (MIMS) method for the on-line analysis of volatile organic compounds (VOCs) in air at low μg/m3 levels was developed. The effects of the thickness of the membrane, the temperature of the membrane inlet and the flow rate of the sample on the responses and response times of some selected VOCs were studied in detail. Under optimised conditions the detection limits for the VOCs studied were 0.5–4 g m−3 and linear dynamic ranges were about four orders of magnitude. Response times of only a few seconds were recorded with a thin (25 μm) membrane. The developed MIMS method was applied to an analysis of air samples from an exhaust of a paintshop, where volatile organic solvents were used.