A new macrolide antibiotic, rosamicin, was shown to have much greater activity in vitro against ureaplasmas isolated from humans than erythromycin or the tetracyclines tested. A marked ureaplasmacidal effect was also shown.Ureaplasma urealyticum has been implicated in both genital disease and infertility in man, but it has not always proved very responsive to available antibiotics and an effective antibiotic treatment is urgently required.BRUNNER et al.1) showed that 57 % of patients with acute or chronic prostatitis were infected with U. urealvticum, compared with only 14%. of healthy controls (ureaplasmas never exceeded 102 colonyforming units per ml in the controls), and they considered it to be the causative organism in 29%of acute and 23 % of chronic cases. GUPTA et al.2) and FRIBERG et al.3) found higher concentrations of ureaplasmas in the genitaltracts of sterile couples than in those of fertile controls.There is evidence that ureaplasmas can be the causative organisms of `non-specific' urethritis.TAYLOR-ROBINSON et al.4) experimentally induced non-specific urethritis in two male volunteers by inoculating a culture of U. urealyticum into their urethras.EVANS et al.5) showed that 10% of ureaplasma isolates were resistant to tetracycline and that all of them were sensitive to erythromycin. Repeated passage increased the resistance to minocycline of three out of four strains. As the concentration required to inhibit growth increased with exposure time, it appears that tetracycline(s) have a static rather than a ureaplasmacidal effect. FORD et al.6) have also reported a case of non-specific urethritis associated with a ureaplasma strain which was resistant to tetracycline but which, however, responded to erythromycin.The findings of SPAEPEN et al.7) were also consistent with those of EVANS et al.5), in so far as they found that increasing concentrations of the four tetracyclines tested were required to inhibit the ureaplasmas examined. Ureaplasmas could, however, be recovered seven days after treatment from 42 % of 50 patients. In contrast to EVANS et al.5) they showed that only 11.4 % of the ureaplasma strains examined were inhibited by 4.0 1sg/ml of erythromycin.A new micromonospora-produced macrolide antibiotic, rosamicin, has shown good results against various mycoplasmas. WAGMAN et al.8), who described it, also tested it against M. gallisepticum, and WALTZ et al.9) examined its activity against four more mycoplasma species. These included four strains of M. pneumoniae, five strains of M. orale, five strains of M. salivarium and one strain of M. hominis.M. hominis was inhibited by 0.4,ug/ml of rosamicin and all other species were inhibited by a concent-

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