Objective: The present study was aimed to evaluate the alterations of maternal serum and amniotic fluid OH-proline levels in neural tube defects (NTD). Methods: 38 patients and 23 control subjects were selected from the patients followed up by the Departments of Genetics and Antenatal Care, Zekai Tahir Burak Women's Health, Education and Research Hospital. Amnion fluid and blood samples were synchronously obtained from NTD and control subjects. OH-proline levels were detected spectrophotometrically. Results: Amniotic fluid CH-proline levels were found to be increased in NTID patients compared to control subjects (p < 0.05). There was no statistically significant difference in serum OH-proline levels between the groups. Conclusion: The results showed an increase in amniotic fluid OH-proline levels in NTD compared to the control group. It may be suggested that the increased OH-proline levels reflect increased collagen turnover in NTD patients. Indeed, amniotic fluid OH-proline levels may be a candidate as an additional diagnostic parameter in NTD. Copyright (C) 2003 S. Karger AG, Basel.