Possible hereditary factors in the tumorigenesis of nasopharyngeal cancer (NPC) have not yet been clearly identified. In the present study, the DNA repair capacity of lymphocytes after exposure to the nitrosamine NDEA was quantified in order to elucidate whether this measure may be a factor in susceptibility to NPC. The alkaline single-cell microgel electrophoresis (Comet) assay was used to quantify chemically induced DNA damage and repair capacity in lymphocytes of 30 NPC patients (NPC) and 29 non-tumor donors (NTD). The induction of DNA single strand breaks, alkali labile and incomplete excision repair sites after exposure of lymphocytes to NDEA was assessed as differences between repair intervals of 0 min, 15 min, 30 min and 60 min, respectively. A RC(total) was assessed using the difference between the OTMs of 0 min of repair time and the 60-min repair interval for both groups. Repair capacities (RC) were calculated for the intervals according to the Olive Tail Moment (OTM), a quantitative measure for DNA migration in the Comet assay for the group of NPC patients and the NTD, accordingly. RCs were compared between the two groups using the Mann-Whitney U-Test. RC(15 min), RC(30 min) RC(60 min) and the RC(total) after a 60-min repair interval demonstrated no significant difference between the two groups. Furthermore, when comparing grades of DNA migration (OTM<2, 2-5, 5-10, 10-20, 20-30 and >30), there were no differences evident. In this investigation, rejoining of DNA single strand breaks in lymphocytes of NPC and NTD appeared to be accomplished to an equal degree and in equal time periods. However, the applied method does not give evidence concerning the quality of the single strand break rejoining processes. In this group of patients, tumorigenesis in NPC could not be associated with a decreased DNA repair capacity.