The frequencies of transduction of the chromosomal genes by pf16 in Pseudomonas putida PgG1 are dependent on the marker transduced and unpredictable. Histidine and isoleucine-valine positive transductants, which are resistant to pf16, have been selected in the crosses with low (about 10(-8) for phage units) frequencies of transduction. Some of these transductants carry new mutations. The transductants are unstable for phage resistance and histidine or isoleucine-valine positive characters. There is no correlation between segregations of the auxotrophic and phage sensitive clones. Among 200 tested mutants of P. putida line PpG1, which were obtained by the direct selection for the resistance of pf16, 3 mutants are found to be auxotrophic for histidine and one mutant unstable for the phage resistance character. The culture medium of such histidine negative and phage resistant mutants as much as phage resistant transductants lyse the lawn of the sensitive to pf16 strains, but viable phages are produced only by those unstable for the phage resistance character. These phages are very similar to pf16 for such characters as host range, size and morphology of plaques, latent period, burst size, transducing ability and the degree of inactivation by pf16 antiserum. The pf16 resistance of mutants and transductants is caused by the disturbing of phage adsorption. Possible mechanisms for the lisogenization of P. putida by pf16 are discussed.