Patterns of urinary proteins were examined on sodium dodecyl sulphate polyacrylamide gels and compared to those obtained using high voltage agarose electrophoresis. Both were found to be well adapted to routine laboratory analysis although the former had more sensitivity for early renal changes. Glomerular, mixed and tubular patterns were identifiable, and special precautions and pitfalls whilst interpreting the latter were pointed out. Restricted alpha 1 antitrypsin was shown in renal transplant proteinuria and its possible mechanisms were discussed. Molecular masses and frequencies of several discrete bands in heavy proteinurics were calculated, and attempts to identify them were made with reference to standard proteins.