Immunoturbidimetry is a suitable technique for the determination of urinary proteins in clinical laboratories. We have developed immunoturbidimetric assays for the measurement of urinary albumin and transferrin which are adapted for the Cobas-BIO centrifugal analyzer. Linear range for the albumin assay was 6.25-167 mg/L and for the transferrin assay 1.66-6.66 mg/L. The analytical recoveries of albumin and transferrin averaged 96%. The addition of up to 50 g/L hemoglobin to urine did not interfere with the determination of either protein. Within-run and between-run imprecision for albumin assay was 2.2% and 3.2% at an albumin level of 140 mg/L, and 4.8% and 8.7% at an albumin level of 16 mg/L; for transferrin assay the respective imprecisions were 3.6% and 6.7% at transferrin concentration of 6 mg/L, and 5.2% and 11.1% at a transferrin concentration of 1.5 mg/L. Reference ranges for both assays were established using urines from 17 healthy individuals; albumin had a range of 0-22 mg/L and transferrin 0-1.9 mg/L.