Purpose: The alteration in the expression of some genes and proteins responsible for chosen DNA repair pathways in pterygium pathogenesis were studied. This study was focused on the examination of the expression of genes and RAD50 protein taking part in homologous recombination. Methods: Peripheral blood lymphocytes, samples of pterygium tissue, samples of conjunctiva of patients suffering from pterygium as well as peripheral blood lymphocytes and conjunctiva of patients from the control group were examined. In order to identify genes products from RNA, Ribonuclease Protection Assai method was applied. LIM15, RAD50, RAD54, RAD52, MRE11, XRCC2, XRCC3, RAD51, RAD51B, RAD51C, RAD51D genes transcripts were detected. Expression of RAD50 protein was analyzed immunohistochemically. Results: Peripheral blood lymphocytes analyses revealed lower level of RAD50 gene expression in the pterygium patients compared to the control group and the increased expression of XRCC2, XRCC3 and RAD51 genes in patients with pterygium, who declared the recurrence of the lesion in comparison to the patients with primary pterygium. Lower expression of the RAD54 gene in pterygium tissue comparing to conjunctiva from the eyes with pterygium was found. An expression of RAD50 gene in the conjunctiva originating from eyes with pterygium in comparison to the conjunctiva of control group was shown to be considerably higher. Expression of RAD50 protein in pterygium squamous epithelial cells was significantly higher than in conjunctiva from control group. Conclusion: There may exist a relationship between pterygium pathogenesis and damages of double strand DNA, however, the elucidation of its exact nature needs further study. [ABSTRACT FROM AUTHOR]