Purpose To evaluate the effect of oxygen pressure during incubation with a B-10-carrier on B-10 uptake capacity of cultured p53 wild-type and mutated tumor cells.Materials and methods Cultured human head and neck squamous cell carcinoma cell line transfected with mutant TP53 (SAS/mp53), or with a neo vector as a control (SAS/neo) was incubated with L-para-boronophenylalanine-B-10 (BPA) or sodium mercaptoundecahydrododecaborate-B-10 (BSH) as a B-10-carrier at the B-10 concentration of 60 ppm for 24h under aerobic (20.7% of oxygen) or hypoxic (0.28% of oxygen) conditions. Immediately after incubation, cultured tumor cells received reactor thermal neutron beams, and a cell survival assay was performed. B-10 concentration of cultured SAS/neo or SAS/mp53 cells incubated under aerobic or hypoxic conditions was determined with a thermal neutron guide tube.Results Hypoxic incubation significantly decreased B-10 concentration of cultured cells with a clearer tendency observed following BPA than BSH treatment in both SAS/neo and SAS/mp53 cells. Following neutron beam irradiation, SAS/mp53 cells showed significantly higher relative biological effectiveness values than SAS/neo cells because of the significantly lower radiosensitivity of SAS/mp53 to -rays than SAS/neo cells.Conclusion Oxygen pressure during incubation with a B-10-carrier had a critical impact on B-10 uptake of cultured tumor cells.