In studies reported in the 1960s and in several investigations since, plasma from irradiated individuals was shown to induce chromosomal aberrations when transferred into normal blood cultures. In the present study, the aim was to investigate the occurrence of these clastogenic factors (CF) using markers representing DNA damage produced in reporter lymphocytes that are treated with plasma from locally exposed individuals. Blood plasma was obtained from clinical patients with benign conditions before and after they had received radiation to small treatment volumes. Three patient groups were studied: (I) marginal resected basal cell carcinoma, (II) painful osteoarthritis of the knee, and (III) painful tendinitis of the elbow or the heel. Patients in each treatment group obtained the same fractionated treatment regimen, ranging from a total dose of 40 Gy (8 × 5 Gy, 2 factions/week) to a very small volume (1-3.5 cm³) in group I to a total dose of 6 Gy (6 × 1 Gy, 2 fractions/week) for groups II and III (treatment volumes 800-1150 cm³ and 80-160 cm³, respectively). The presence of CF in the plasma was investigated through cytogenetic (chromosomal aberrations, micronuclei) assays and kinetics of early DNA damage (γ-H2AX foci) in reporter cells. With the experimental settings applied, local radiation exposure had no apparent effect on the induction of CF in patient plasma; no deviations in chromosomal aberrations or micronucleus or focus induction were observed in reporter cells treated with postexposure plasma with respect to pre-exposure samples when the mean values of the groups were compared. However, there was a large interindividual variation in the plasma-induced DNA-damaging effects. Steroid treatment of patients was demonstrated to be the most influential factor affecting the occurrence of plasma factors; plasma from patients treated with steroids led to significant reductions of γ-H2AX foci and reduced numbers of chromatid aberrations in reporter cells. In addition to the locally exposed patients, newly obtained plasma samples from three radiological accident victims exposed in 1994 were examined. In contrast to the patient data, a significant increase in chromosomal aberrations was induced with plasma from two accident victims.