The effectiveness of neutrons from a californium-252 source in the induction of various abnormalities in the Tradescantia clone 4430 stamen hair cells (TSH-assay) was studied. Special attention was paid to check whether any enhancement in effects caused by the process of boron neutron capture is visible in the cells enriched with boron ions. Two chemicals (borax and BSH) were applied to introduce boron-10 ions into cells. Inflorescences, normal or pretreated with chemicals containing boron, were irradiated in the air with neutrons from the ²⁵²Cf source at KAERI, Taejon, Korea. To estimate the relative biological effectiveness (RBE) of the beam under the study, Tradescantia inflorescences without chemical pretreatment were irradiated with various doses of X-rays. The ranges of radiation doses used for neutrons were 0-0.1 Gy and for X-rays 0-0.5 Gy. After time needed to complete the postirradiation repair Tradescantia cuttings were transferred to Krakow, where screening of gene and lethal mutations in somatic cells of stamen hairs have been done, and dose response relationships were plotted. In two independent experimental studies an alteration of dose-response curves was observed, probably due to slight changes in the postexposure plant treatment. However, it has not resulted in the change of the maximal RBE values, which for the induction of gene mutations were estimated as 5.6 in the pilot studies, and 5.8 one year later. Inflorescences pretreated with borax and BSH responded to neutrons differently. The values of RBE have changed from 5.6 to 7.9 in the case of plants pretreated with 240 ppm of B-10 from borax, and 5.8 to 7.2 in the case of 400 ppm of B-10 from BSH. The results showed an increase, although statistically insignificant, in biological efficiency of radiation from the ²⁵²Cf source in the samples pretreated with boron containing chemicals.