The analysis of urinary proteins and their identification are discussed, particularly in regard to the technique of sodium dodecyl sulphate electrophoresis in polyacrylamide gradient gels. Urine collection, storage and preparation are evaluated, especially in regard to problems connected with concentration and dialysis of such samples. The instrumental approach to sodium dodecyl sulphate polyacrylamide gel electrophoresis represented by the Phast System appears to be particularly valuable in routine clinical analysis of urine specimens, since no sample pretreatment is required. The following types of proteinurias are evaluated: (a) orthostatic proteinurias; (b) post-renal proteinurias; (c) Bence-Jones proteinuria; (d) lower and upper urinary tract infection (cystitis and pyelonephritis) and (e) diabetes mellitus proteinurias.