Aerobic bacterial isolates obtained from endocervical, vaginal and urethral swabbings were tested for interference of neisseria gonorrhoeae growth on solid medium. Simultaneous antagonism was studied using the lawn spotting method, and delayed antagonism by the basal spot/lawn method. From 58 swabbings we recuperated a total of 181 isolates, 71 of those were found interfering with at least one out of four gonococcal strains (G-1, G-2, G-3 and G-4). Similar percentages of interfering isolates were obtained from each of the isolation sites. The identification of the interfering isolates has revealed that similar numbers of coagulase negative staphylococci and identical numbers of group D streptococci were found for each of those sites. The majority of the interfering isolates and also of the inhibitory coagulase negative staphylococci showed only simultaneous antagonism. To complete the interference spectrum, we have tested all the active urogenital isolates against four other gonococcal strains (G-7, G-9, G-10 and G-11). This spectrum showed clearly that interference is not an all or none phenomenon. While the gonococcal interference spectrum of most of the Gram positive cocci and the Acinetobacter sp. strains is broad, that of all the other isolates is relatively narrow. Gonococcal strains G-7 and G-9 were the most susceptible to inhibition by the interfering urogenital isolates while strain G-3 was the most resistant one.