The effect of inoculum size and nutrients on bacterial growth was examined using a Biophotometer (Jouan, Paris). The inoculum size greatly affected the length of lag time but not the growth rate. There were two types of reduction of lag time. In one the lag time was reduced regularly in parallel with an increase in inoculum size, and in the other the lag time was reduced irregularly. Composition of the media and supplementation of nutrients influenced the reduction of lag time, but the effect of compounds used were varied from strain to strain. Among the compounds employed, no common substance was found that would change an irregular reduction of lag time to a regular reduction of lag time with an increase of inoculum size. Reduction of lag time when inoculum size was increased ten times was termed L10, and a simple calculation of doubling time is discussed on the basis of cell number in the inoculum and L10.