In an attempt to study the composition of the Lactobacillus flora from mucosa of human stomach, 16S rRNA gene sequences of 129 isolates were analysed. For 15 of these, the results differed significantly from known sequences, and additional tests were performed to determine whether these isolates represented as yet unrecognized species. Phenotypic and genetic characteristics revealed that these isolates represented four novel Lactobacillus species. Two belong to the Lactobacillus reuteri and the other two to the Lactobacillus delbrueckii subgroup of Lactobacillus. The names Lactobacillus gastricus sp. nov., Lactobacillus antri sp. nov., Lactobacillus kalixensis sp. nov. and Lactobacillus ultunensis sp. nov. are proposed, with the respective type strains Kx156A7T (=LMG 22113T=DSM 16045T=CCUG 48454T), Kx146A4T (=LMG 22111T=DSM 16041T=CCUG 48456T), Kx127A2T (=LMG 22115T=DSM 16043T=CCUG 48459T) and Kx146C1T (=LMG 22117T=DSM 16047T=CCUG 48460T).