Cervical and urethral specimens from 247 females were cultured for T-mycoplasmas. The occurrence of T-mycoplasmas in clean-voided, mid-stream and catheterized urine specimens was also investigated. There was no significant difference in the recovery rate of T-mycoplasmas in the genito-urinary tract between healthy non-pregnant women and women with signs of genital infections (45.8 and 55.4 per cent respectively). In healthy, pregnant females the incidence of T-mycoplasmas was significantly higher, or 68.4 per cent. In women taking oral contraceptives, T-mycoplasmas were found more frequently than in women of comparable ages and groups not taking oral contraceptives. Prepubertal girls and postmenopausal women had a low incidence of T-mycoplasmas (8.0 and 4.3 per cent respectively). T-mycoplasmas were cultured from 15.4 per cent of catheterized urine specimens collected from women harbouring these organisms in the urethra, while the corresponding figure in clean-voided, mid-stream urine specimens was 84.9 per cent. This study indicates that T-mycoplasmas occur as commensals in the female genital tract. The hormonal status of the individual seems to be an important factor for their occurrence. T-mycoplasmas often occur in urine specimens as contaminants from the urethra or the vulva. Sampling from the urethra or the cervix is more reliable than collection of urine for the demonstration of T-mycoplasmas in the female genito-urinary tract.