Certain fastidious organisms such as U urealyticum and G vaginalis can be isolated from the aspirated bladder urine of pregnant women more frequently than conventional urinary pathogens such as Escherichia coli [1]. They can be isolated even more often from the aspirated bladder urine of patients with renal disease, but rarely from that of healthy men or nonpregnant women [2]. We investigated the incidence of bacteriuria due to these two organisms--particularly U urealyticum--in patients with preeclampsia. U urealyticum was isolated more frequently (rate, 20%), and usually in higher colony counts, from the urine of patients with preeclampsia than from that of healthy pregnant women (rate, 7%). G vaginalis was isolated with approximately the same frequency as U urealyticum from specimens of bladder urine; both organisms were isolated from the urine of 11 patients (eight healthy women and three with preeclampsia). High colony counts of G vaginalis were also found more frequently in patients with preeclampsia. In both groups other fastidious organisms were isolated in a total of only five patients, and in four of these five cases U urealyticum and/or G vaginalis were also isolated from the same specimen. Urine cultures were more frequently positive in patients with moderately severe hypertension (blood pressure, greater than 160/100 mm Hg) than in those with mild hypertension (blood pressure, 140/90-160/100 mm Hg, occurring in nine (53%) of 17 patients and in nine (26.5%) of 34 patients, respectively. This difference was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)