A microscopy method was developed to analyze lag phase durations (tLag) of individual 'Listeria monocytogenes' cells. Results were compared with mean individual cell lag times (tL) using the Bioscreen. Lag values from microscopy and Bioscreen are related by the equation: tLag = tL + DT (where DT = doubling time). Individual lag times measured by both methods were normally distributed. A further investigation on the effect of low pH values (pH 6, pH 5.5 and pH 5) was undertaken using the microscopy method. At pH 6, lag times fit a lognormal distribution well ([chi]2 = 0.29), with a mean lag time of 2.54 ± 0.71 h. At pH 5.5, lag times also fit a lognormal distribution ([chi]2 = 0.54), with a mean lag of 3.04 ± 0.92 h. At pH 5, the graph of the lag time distribution showed two peaks, and lag times did not fit a lognormal distribution well ([chi]2 = 0.98).