OBJECTIVE In the general population there is association between Chlamydia trachomatis (Ch. trachomatis) infection and reactive arthritis (RA). RA is a systemic illness characterized by inflammatory synovitis. Arthritis tends to be oligoarticular and involves mainly the lower limbs. The aim of this study is to assess the age and sex specific prevalence of Ch. trachomatis infection in dialysis population and to find possible relationship between manifestation of infection and renal osteodystrophy. METHODS The study was conducted in 53 patients: 22 women (W) and 31 men (M), with a mean age of 58.1 +/- 15 years, treated with HD for 28.5 +/- 28.2 months. The Ch. trachomatis infection was assessed by the detection IgG antibodies for Ch. trachomatis. Also some other biochemical parameters of osteodystrophy, inflammation and malnutrition were measured. RESULTS The presence of a high titre of anti-Ch. trachomatis antibodies was found in 22 patients--41% [G IgG (+)]. Mean level of anti-Ch. trachomatis antibodies was significantly higher in G IgG (+) than in seronegative patients [G IgG (-)]: 19.0 +/- 8.6 vs 4.0 +/- 2.1 U/ml, p<0.001. There was no difference in mean age of seropositive and seronegative patients for Ch. trachomatis (62.4 +/- 13.1 vs 56.2 +/- 15.9 years). We did not observe in both groups of patients any differences in mean level of C-reactive protein (CRP): 12106.2 +/- 10791.0 vs 14015.3 +/- 11194.3 ng/ml. The mean ferritin level was significantly higher in G IgG (+): 624.3 +/- 375.7 vs 418.3 +/- 341.4 ng/ml, p<0.05. Significant negative correlations were found in G IgG (+) between IgG antibodies and transferrin saturation (r=-0.645719, p<0.001) and between CRP and calcium (r=-0.4526, p<0.05). IgG antibodies were detected frequently in W (60%) than in M (29%). Mean level of IgG was significantly higher in seropositive W than in seropositive M (23.3 +/- 7.8 vs 12.1 +/- 4.2 U/ml, p<0.0001). The seropositive W were older (67.9 +/- 11.8 vs. 53.8 +/- 11.0 years, p<0.02) and seropositive W were shorter treated with HD (18.1 +/- 16.6 vs 43.7 +/- 30.6 months, p<0.02). The mean serum calcium conc. and phosphorus were significantly lower in seropositive W (2.1 +/- 0.1 vs 2.3 +/- 0.2 mmol/l, p<0.05 and respectively 1.3 +/- 0.3 vs 1.8 +/- 0.2 mmol/l, p<0.005). Likewise the mean transferrin saturation (TS) was significantly lower in that group (25.7 +/- 7.3 vs 38.0 +/- 11.3%, p<0.01). There were no differences between seropositive men and women in mean serum concentrations of CRP, iPTH, albumin and hemoglobin. We found in seropositive W significant negative correlation between IgG antibodies and age (r=-0.633, p<0.02). CONCLUSIONS The patients treated with HD were quite frequently shown significantly elevated level of IgG antibodies for Ch. trachomatis. It could have be connected with past infection. The antibodies were more commonly detected in women, particularly in younger patients. No relationship between osteodystrophy and Ch. trachomatis infection was found.