The authors examined 79 patients (n = 79) with primary and secondary osteoporosis incl. 31 men (nM = 31) aged 31–61 years and 48 women (nF = 48) aged 33 to 65 years. In these patients the authors investigated the aminoterminal telopeptide of collagen I of the organic bone matrix (NTx) on the 24-hour (NTx 24) and 2-hour morning (NTx 2) diuresis (from 6 to 8 a.m.). Objective: to find a reply to the question 1. Is there a statistically significant correlation between values BTx in the 24-hour and 2-hour diuresis in patients with osteoporosis? 2. Is there a statistically significant difference in the level of NTx in the 24-hour and 2-hour diuresis in the same patient? 3. Is the 2-hour diuresis more accurate for the assessment of levels of NTx in patients with osteoporosis than the hitherto used collection of the first or second urine sample collected at any time in the morning? Statistical analysis: for testing of the normality of distribution in each group the authors used d’Agostin’s test. The one way relationship of a random variable y (NTx 2) on the independent variable x (NTx 24) was expressed by linear regression. Results: Between values NTx (axis x) and NTx 2 and NTx 1 (axis y) a significant (p < 0.001) positive correlation was found (women r = 0.884, men r = 0.593). In the group of men and women significantly higher values of NTx 2 were found than NTx 24 which is due to the circadian biorhythm of the NTx level which reaches its excretory maximum between 3 and 7 a.m. The reference value of NTx 2 calculated from the equation of linear regression [y = a + bx, b = NTx 2, x = NTx 24, (a, b) – regression coefficients] have a narrower interval (women: 22.96–46.48 nmol/mmol creatinine, men 29.52–47.16 nmol/mmol creatinine than the reference value for the first morning urine given by the manufacturer of NTx kits (OSTEX USA) – women 5–65, men 10–72 nmol/mmol creatinine). Conclusion: 1. Between values of NTy 24 and NTx 2 a significant positive correlation was found. Both urine samples can be used for assessment of NTx levels. 2. Introduction of two-hour morning diuresis for assessment of NTx levels reduces the range of variation of NTx levels during repeated examinations and makes the information provided by the values more accurate.

        Key words: NTx, osteoresorption, diuresis, osteoporosis