Summary The incidence of asymptomatic bacteriuria in 1160 patients screened in early pregnancy was 4·6%. This finding was based on the examination of a single midstream specimen of urine. The incidence of bacteriologically confirmed urinary-tract infection developing during pregnancy in the whole group was 4·1% and in the bacteriurics 16·6%. Only 19·1% of patients who developed an acute urinary infection during the pregnancy had bacteriuria on initial screening. The value of screening for bacteriuria as a method of preventing acute pyelonephritis is therefore questioned, and it is suggested that laboratory resources might be better concentrated on the follow-up of patients who develop a proven infection during pregnancy.