Using a previously developed bioassay, the sensory and pulmonary irritating properties of a group of 10 aerosolized machining fluids were evaluated in mice. Single, 3-hr inhalation exposures were conducted with the fluids at exposure concentrations ranging from 20 to 2000 mg/m3. The results have shown that all 10 were capable of inducing sensory and pulmonary irritation, with little or no change in pulmonary histopathology. A concentration-response relationship was developed for each fluid which revealed that, for the 10 fluids studied here, the synthetic/semisynthetic and soluble fluids were more potent irritants than the straight oils. Also, 3 of the 10 fluids which had been collected from workplace operations (i.e., "in use" fluids) were found to be similar in potency to the same fluids prior to their introduction into the workplace (i.e., "neat" fluids). From concentration-response relationships, the RD50 value (i.e., concentration inducing a 50% response) was obtained for each of the 10 fluids. The RD50 values ranged from 100 to 1000 mg/m3 for all fluids except the straight oils whose RD50 values were over 100,000 mg/m3. Using these values, exposure limits were then suggested for workers in industry to prevent irritation. This bioassay may be a good first step in evaluating new machining fluids whose formulations may change depending upon the current industrial needs.