Characteristics of genomic DNA of Lactobacillus spp. and Bifidobacterium spp. were determined by pulsed field gel electrophoresis and the following results were obtained; Four enzymes, Sma I, Apa I Not I and Sfi I were identified as suitable for generation of relatively few numbers of distinct fragments from the Lactobacillus spp. genomes, whereas five enzymes, Sma I, Apa I, Sfi I and Dra I were suitable for Bifidobacterium spp. genomes. The genome sizes of Lactobacillus spp. ranged from 1.S8Mb to 3.31Mb, the genome sizes of L. brevis ATCC 8287, L. fermentum ATCC 14931, L. casei YIT 9018, L. plantarum KCTC 1048 and L. delbruekii subsp. delbruekii ATCC 9469 were estimated to be 1.93Mb, 1.98Mb, 2.84Mb, 2.81M6 and 1.82Mb, respectively. Those of Bifidobcxterium spp. ranged from 1.85Mb to 2.83Mb. The genome sizes of B. bifrdum ATCC 29521, B. longum ATCC 15707, B. infantis ATCC 15697 and B. bifidum CU 1370 were estimated to be approximately 1.85Mb, 2.83Mb, 1.86Mb and 1.94Mb, respectively.