[en] The authors used a human lymphoblastoid cell line (W1L2-N5) to examine the molecular structure of mutations occurring at an autosomal locus together with some of the mechanisms possibly involved in mutation induction by radiation. Results indicate that a very high fraction of mutations induced by x-rays result from large scale changes involving loss of the entire active gene and often extending to other loci on the same chromosome. Preliminary results suggest that mitotic recombination may be an important mechanism for radiation mutagenesis. (UK)