SUMMARY: Phage N6 lysates of Micrococcus lysodeikticus and Sarcina lutea were very viscous and were found to mediate genetic transfer of an adenine marker (ade+) to adenine-dependent strains of M. lysodeikticus. The transfer activity of these lysates was found to reside in a high molecular weight DNA fraction rather than in the phage particles themselves. DNA that was isolated and purified from phage lysates and lysozyme-treated cells was shown to possess transforming activity. Recipient competence was maximal during late logarithmic growth (14-18 hr). The cell density of the transfer suspension was optimum at about 107 colony forming units/ml. Transformants were recovered after 1 hr exposure to DNA and continued to increase in number up to 6 hr. Transformants appeared in higher frequencies on Difco agars that were less purified. Under optimal conditions, transformation frequencies up to several percent per colony forming unit were obtained. All strains of M. lysodeikticus tested (ATCC 4698, ATCC 15801, CCM 1335, PU, UM, WRU, ISU) could serve as donors of the ade+ marker. All strains, except ATCC 4698, were competent recipients of the adenine marker.