1. The ratio of albumin clearance to creatinine clearance (CA/CC) was determined on 129 occasions in forty patients with a wide variety of renal diseases, both 24 h collections of urine and random mid-morning samples being used. The clearance ratios derived from 24 h urine (24 h CA/CC) and random urine (R CA/CC) were compared with random urine protein concentration, 24 h urine protein excretion and 24 h urine albumin excretion.

2. From these measurements 24 h CA/CC could only be predicted accurately by R CA/CC, particularly when patients with postural proteinuria were excluded.

3. The diurnal variation of CA/CC was investigated in twelve patients with renal disease. The individual values for CA/CC obtained throughout the day were within the limits of prediction of 24 h CA/CC already established. The diurnal variation of CA/CC was considerably less than that of CA or CC alone and also less than that of the rates of protein and albumin excretion.

4. It is suggested that CA/CC is the best readily available measure of ‘glomerular leakiness’ and examples are given of its clinical value. In patients with renal disease 24 h CA/CC could be predicted, in this study, from the clearance ratio based on simultaneous random urine and blood samples.

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