Spacer regions between the 16S and 23S rRNA genes of different dairy and probiotic lactic acid bacteria were amplified by the polymerase chain reaction (PCR) with conserved primers and the nucleotide sequences of these spacer regions were determined. Amplification/oligonucleotide primer pairs were designed for Lactobacillus paracasei, Lactobacillus rhamnosus, Lactobacillus delbrueckii, Lactobacillus acidophilus, Lactobacillus helveticus and Streptococcus thermophilus based on the differences in the nucleotide sequences of the 16S-23S rRNA spacer regions. Also a primer pair identifying both Lb. paracasei and Lb. rhamnosus was designed. In addition to conventional PCR in a heat block a rapid PCR method in an Air Thermocycler (ATC) with glass capillaries was used.