A new selective medium (CBU agar) was compared with blood agar (BA) medium for primary isolation of Corynebacterium urealyticum from urine and skin samples of hospitalised patients. Overall, the CBU agar detected C. urealyticum in 14 (4.6%) of 302 urine samples and the BA medium detected the organism in four (1.3%), but most cultures which were positive only on CBU agar had < 10(4) cfu/ml. Six strains of C. urealyticum were isolated from 60 skin samples with CBU agar, whereas none was detected with BA. Although most skin samples had heavy inocula, the selective agar facilitated the recognition of low colony counts (< or = 10 cfu/plate) of C. urealyticum by reducing the growth of competing flora. Challenge of the selective medium with reference and clinical strains showed that CBU agar was inhibitory for gram-negative bacteria and reduced the gram-positive flora, allowing the growth of C. urealyticum strains. The new selective medium appears to be a useful epidemiological tool to study urinary and skin colonisation by C. urealyticum.