['To study the role of transforming growth factor beta1 (TGF-beta1) on cellular radiation sensitivity by analysing mouse lung fibroblasts of different TGF-beta1 genotypes.', 'Heterozygous TGF-beta1 knock-out mice were mated to produce offspring of different TGF-beta1 genotypes as confirmed by PCR-genotyping. Primary lung fibroblast populations were established from new-born animals of specific genotypes (TGF-beta1(+/+), TGF-beta1(+/-), TGF-beta1(-/-)). Production of TGF-beta1 was tested by ELISA. TGF-beta1 receptor-II mRNA expression was analysed by RT-PCR. Colony formation of untreated, TGF-beta1-treated and/or irradiated primary lung fibroblasts was determined under different medium conditions.', 'Plating efficiencies under different medium conditions were independent of TGF-beta1 genotype. Production of TGF-beta1 correlated with the genotype: heterozygous TGF-beta1 knock-out fibroblasts (TGF-beta1(+/-)) produced 60-65% of wild-type (TGF-beta1(+/+) cells). As expected, homozygous TGF-beta1 knock-out fibroblasts (TGF-beta1(-/-)) did not produce TGF-beta1. Radiation exposure significantly enhanced TGF-beta1 production in TGF-beta1(+/+) cells by a factor of 2. No such stimulation was observed in TGF-beta1(+/-) cells. TGF-beta1(+/-) and especially TGF-beta1(-/-) cells were significantly more radioresistant than TGF-beta1(+/+) cells. TGF-beta1 treatment significantly reduced clonogenic survival for both TGF-beta1(+/+) and TGF-beta1(-/-) cells. TGF-beta1 treatment of TGF-beta1(-/-) cells resulted in an enhancement of radiation sensitivity.'] Do irradiated homozygous TGF-beta1 knockout fibroblasts show enhanced clonogenic survival as compared with TGF-beta1 wild-type fibroblasts?