The rRNA-targeted oligonucleotide probes are useful for the identification of Lactobucillus acidophilus, L. gasseri, L. johnsonii, L. crispatus, and L. amylovorus. However, the oligonucleotide probe designed for L. helveticus hybridized with nucleic acids of type strains of L. gallinarum and L. helveticus. Hence, the similarity among the 73 strains of lactobacilli was evaluated on the basis of their randomly amplified polymorphic DNA (RAPD) profiles derived from five single-primer reactions. These strains were grouped into seven clusters at a similarity level of 30%, which corresponded to six separate species of the L. acidophilus complex (L. johnsonii, L. gallinarum, L. amylovorus, L. crispatus, L. acidophilus, and L. gasseri, respectively) and L. helveticus. For the first time, strains of L. gallinarum were characterized by RAPD and PFGE analyses. The genome length in that species was estimated to be near 1.45 Mb with the summation of ApaI fragments, and near 1.95 Mb with the summation of SmaI fragments.