Five cases of marble bones in two families living near Brescia are presented. Case 1 (42-yr-old female) was a typical malignant form with deep and extensive eburnation, many pathological fractures, concomitant osteitis and the formation of many fistulae, massive spleen enlargement and infarct, and marked anaemia with clear signs of extra-medullary haemopoiesis. The patient died 5 yr after her first admission. Two of her brothers had had an identical, fatal form. Case 4 (28-yr-old male) was much the same: virtually general osteosclerosis despite the difference in age, marked spleen enlargement, a history of fractures, serious anaemia and extramedullary haemopoiesis. Benign pictures were seen in cases 2 and 3 (73- and 68-yr-old females). In case 5 (25-yr-old male), typical bone condensation was the only significant pathological sign. It is suggested that this, too, may be seen as a "benign" form.