Some new, generally nonchemotactic mutants of Salmonella typhimurium were isolated and they, together with previously isolated mutants and some from other investigators, were mapped. Most of the mutants were classified in nine complementation groups, which are probably individual genes. Of these, five map at the end of the flagella region and appear in the order motB-(cheWcheP)-cheX-cheQ-cheR-flaC. Two of the mutations, cheU and cheV, map in the flaQ and flaAII genes, respectively. The remaining genes, cheS and cheT, have not yet been mapped. Most of the mutants are phenotypically smoothly swimming, but some are constantly tumbling. Two of the groups show dominant behavior as recipients in genetic crosses; the rest are recessive. The mutants vary in their responses to stimuli but, since their responses to all chemoeffectors are abnormal, the central processing, rather than individual, receptors must be impaired. The two mutations that coincide with genes for flagella probably involve the locus of the final delivery of sensing signal to the flagella.