Stone analyses (kidney, upper urinary tract) of the department of Urology, University of Erlangen, from a four-year-period (1974-1977) have been recorded with emphasis to stone composition, sex and age of the pertinent stone forming patients. During this time period there were no substantial changes as regards the per cent frequency of the various stone types. The most frequent type was calcium oxalate (CaOx), followed by uric acid, calcium phosphate (CaP), struvite and cystine. Stone analyses were mostly requested for patients between 46 and 55 years of age. Stone incidence in our clinic is calculated to be 1.22 times higher in males than females, especially beyond 36 years of age. The frequency peaks are: pure (= 100 per cent) CaOx 36-45 years; CaOx with additional mineral phases (mostly CaP) 46-55 years; uric acid 56-65 years; CaP 26-35 years. From those patients who underwent further investigations in searching for metabolic abnormalities serum concentrations, urine mineral clearances in fasting urine samples, and activity products of stone forming mineral phases in sequentially collected specimens from 24 h and 2 h fasting urine had been measured and compared with values from healthy control subjects. In urolithiasis (idiopathic) there is a normal parathyroid hormone blood level, a generally lower serum inorganic phosphate and magnesium concentration. In pure (= 100 per cent) CaOx and uric acid lithiasis serum uric acid and creatinine are higher than in controls, urine pH and calcium clearance in some groups are different too. Clearances of magnesium, uric acid, phosphate, sodium are within normal limits in urolithiasis. When expressing the propensity to form stones in terms of activity products, then only uric acid lithiasis deviates substantially from normal. All other stone types differ only slightly or not at all from each other and controls respectively. It is concluded that 1) in our geographic region the various stone types prevail in different age periods; 2) there are distinct alterations of parameters of mineral metabolism in urolithiasis; 3) measuring urine clearances may lead to assume falsely normal mean urine excretion of stone forming constituents.