Albumin excretion rates (AER) of three consecutive days in different urine collection periods were measured in 7 hospitalized microalbuminuric diabetics (Ma DM) and 7 normoalbuminuric diabetics (Na DM). They were divided on the basis of an initial overnight urinary AER below or above 10 micrograms/min. The percentage of variation coefficients (% CV) of 24-hour, overnight 12-hour, and morning one-hour urine collections in Ma DM were 29.9%, 31.8% and 50.9%, respectively; while in Na DM group were 60.0%, 60.3% and 74.5%, respectively. There was no significant difference in the variation of AER among the three different urine collection procedures in both Ma DM and Na DM groups, or for similar urine collection between the two groups. The initial AER was compared to the subsequent two AERs in overnight 12-hour collection. The results were that three Ma DM patients had a subsequent AER below 10 micrograms/min and two Na DM patients had a subsequent AER above 10 micrograms/min on a single occasion. Therefore, the high variability of both groups would be expected to result in category changes. Multiple urine collections are needed to detect the early diabetic nephropathy for the hospitalized diabetics.