The results of two mutagens are presented in order to demonstrate the sensitivity of a modified Salmonella microsuspension assay (Kado et al. 1983) compared to the standard plate-incorporation assay. The first procedure was 2.4-7.3 times more sensitive in detecting the mutagens, 2-aminoanthracene and sodium 5-(3-nitro-2-furyl)acrylate. Methanol extract and cyclohexane extract from cigarette side smoke enhanced the response in the absence and presence of S9 activation mixture with the TA 98 strain. The cigarette side smoke mutagens were detected in 10 times lower volume samples (0.1 m3 of sampled air) in the microsuspension assay than in the plate incorporation assay.