While studying a set of multiply marked mutants of Staphylococcus aureus strain 8325 by transformation, several instances of apparent genetic linkage were encountered. After showing that these linked transformations were readily inactivated by shearing of the deoxyribonucleic acid (DNA) but were resistant to dilution of the DNA, and showing that mixtures of DNA failed to form double transformants, it was concluded that the linkages were legitimate rather than the result of congression. Three linkage groups were defined: thy-101-lys-115-trp-103-thr-106, pyr-141-hisGb15-nov-pur-102, and pur-110-ilv-129. The positions of the previously studied trp and his operons corresponded to the trp-103 and hisGbl5 loci. The ilv-129 position adjacent to pur-l10 probably corresponds to the ilv-leu gene cluster. The distance over which linkage was detected was greater by transformation than by generalized transduction. 201 on August 11, 2020 by guest http://jb.asm.org/ Downloaded from for 30 min on a Burrell wrist-action shaker (Burrell distilled (under N2) phenol saturated with 0.01 Corp., Pittsburgh, Pa.). The lysis mixtures were then M Tris(hydroxymethylfaminomethane-hydrochloride extracted three times with equal volumes of freshly buffer, pH 8.