the total hydroxyproline excretion in urine was investigated in 82 patients with hyperthyroidism without data fro a concomitant disease, 50 clinically healthy subjects with euthyroid struma, 10 patients with non endocrine froms of osteoporosis, 4 diabetics with not stable diabetic compensation and 4 patients with primary hyperparathyroidism. The average hydroxyproline values, in the patients with active thyreotoxicosis in 24 hours urine are 56.01-6.03 mg and 16.74 +/- 7.38 mg, after reaching the therapeutic remission. The excretion is with an average of 17.52 +/- 6.03 mg in the patients with euthyroid struma. In patients with primary hyperoparathyroidism-121.60 +/- 18.2 and in patients with diabetes mellitus-51.10 +/- 3.11, in the subjects with osteoporosis-25.83 +/- 10.88 mg. The differences between the patients with active hyperthyroidism and euthyroid struma, as well as after coming to a terapeutic remission are statistically highly significant.