Abstract: A process for sampling ambient air at a work place comprises continually withdrawing by means of a pump, a sample of ambient air in the proximity of the respiratory tract of an individual worker, filtering the aspirated air for subsequent analysis of filtered-out particles, picking-up the cardiac rhythm of the individual and controlling the flow of air of the pump by a signal modulated by the cardiac rhythm of the individual. Apparatus for carrying out the process copmrises a sampling tube, a motor driven pump for drawing a sample of ambient air in through the sampling tube, a filter associated with the sampling tube for filtering the air sample, a photo electric device for picking up the cardiac rhythm of the individual and a control circuit for controlling the flow-rate of the pump by a signal modulated by the cardiac rhythm of the individul. The pump motor is further controlled by a pressure pick-up downstream of the filter to correct for flow attenuation by the filter.