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XP3BR is a fibroblast strain derived from a xeroderma pigmentosum patient exhibiting severe mental retardation in addition to the typical changes in the skin. No tumours have been observed by 6 years of age. Cells from this patient had no detectable excision repair of u.v. damage. The defect in daughter strand repair was also characteristic of excision-defective XP's. The material was assigned to complementation group G and is the second (unrelated) example from this group. XP3BR cells were more sensitive than normal cells to the lethal action not only of u.v. but also of gamma irradiation, in contrast to all other XP cells tested to date including XP2BI, the other representative of complementation group G. The u.v. sensitivity was similar to that of strains from complementation groups A and D, confirming the correlation between extreme u.v. sensitivity and the presence of neurological defects. Following treatment with u.v., XP3BR, and other XPs gave more 6-thioguanine resistant mutants than normal cells whether the comparison was made per unit of dose or per lethal event. After low doses of gamma irradiation XP3BR cells were more mutable than normal or XP2BI cells.

We describe an otherwise healthy mother and son who have developed Jessner/Kanof’s lymphocytic infiltration of the skin. This is the first description of this condition occurring in a parent and child in this fashion.

Summary Pyoderma gangrenosum may occur in patients with haematological disorders but has not frequently been reported in patients with polycythaemia rubra vera. To support the view that this is a significant association, we report a further two cases and discuss the implications of the development of pyoderma gangrenosum in patients with polycythaemia.