1. A case of osteoid osteoma which recurred twice after block excision is reported.

2. It is postulated that recurrence is almost certainly caused by incomplete removal of the nidus, either by curettage or by incomplete block excision.

3. Why curettage is successful in most cases but not in others is obscure, but it may be that the arterial supply to the tumour is interrupted.

4. Block excision with adequate radiographic control to ensure its completeness is the treatment of choice.

1. The case histories of four siblings affected by osteogenic sarcoma are described.

2. The lesions appeared over a period of twelve years. The ages of the patients at the onset of symptoms were fifteen, twenty, eleven and twenty-two years.

3. The diagnosis of osteogenic sarcoma was in each case established by radiological and histological methods.

4. Two patients survived for eight and sixteen years after treatment and both are still alive and well.

1. Three cases of a benign osteoblastic lesion of bone are described. An outstanding feature of each was the hyperostosis of adjacent bones or synovitis in an adjacent joint.

2. The clinical, radiological and histological features resembled osteoid osteomata more than benign osteoblastoma in each case.

3. The significance of this observation is questioned in relation to the pathogenesis of osteoid osteoma.

1. Two cases are reported in which reappearance of an osteochondroma after excision was shown to represent a second independent lesion and not a true recurrence.

2. The significance of this observation is discussed in relation to the pathogenesis and prognosis of this lesion.

3. A plea is made for greater discrimination in using the ominous description "recurrence," because the rare true recurrence must strongly favour a diagnosis of malignancy.

1 . Six patients have been presented in whom an established diagnosis of non-osteogenic fibroma of bone was made. Metaplastic bone was identified within the tumour tissues.

2. Three other patients are reported in whom the diagnosis appeared to be, on radiological and histological grounds, either fibrous dysplasia or non-osteogenic fibroma.

3. This evidence has convinced the author that the two lesions are frequently not distinctive and that they are, in fact, closely related. Because the natural history of the two conditions, especially in their simple or monostotic form, is also the same, there is good reason to consider them as varying histological manifestations of the same pathogenetic process.

1. Two cases are reported in which hyperkalaemia was a prominent feature in acute renal failure and in which obvious sources of excess potassium were apparent.

2. The literature pertaining to potassium in acute renal failure is briefly reviewed.

3. A return to the surgical elimination of large and expendable tissue sources of potassium in the management of acute renal failure with hyperkalaemia is suggested.