The value of Micro-Bumintest tablets and the albumin/creatinine ratio in first morning (FM) urine samples to screen for micro-albuminuria in diabetic patients was evaluated. The A/C ratio in FM urine was highly correlated with the urinary albumin excretion (UAE) rate in micrograms/min in timed overnight (0) urine (R = 0.95, p < 0.001). The sensitivity, specificity and positive and negative predictive values of an A/C ratio > 3.0 to predict micro-albuminuria defined as an UAE > 20 micrograms/min were 94, 92, 92 and 94% respectively. The day-to-day fluctuation of albumin excretion varied between 10 and 105%. The sensitivity, specificity and positive and negative predictive values of micro-bumintest tablet reactions on FM urine samples to predict an A/C ratio > 3.0 were 93, 59, 63 and 91% respectively. It is concluded that for screening of micro-albuminuria the A/C ratio in FM urine is as precise as timed 0 urine collection, but with more comfort for the patient. Micro-Bumintest tablets are useful as an initial screening test and will decrease the number of quantitative albumin measurements in the screening programme by about 30% if only urine samples with positive tablet test are selected for a further investigation. Because of considerable day-to-day fluctuation of urinary albumin excretion several urine samples should be investigated before presence of incipient diabetic nephropathy is assumed.