Iliac-crest bone biopsies were performed on 20 consecutive patients presenting to a rheumatology clinic with bone pain and/or pathological fracture on X-ray examination. Four patients had osteoarthrosis, ten patients rheumatoid arthritis and six patients back pain. Quantitative bone pathology showed seven patients to have osteomalacia, four patients osteoporosis, and two patients both osteomalacia and osteoporosis. Blood chemistry was of little help in diagnosis though a very high alkaline phosphatase was found in patients with Paget's disease and unsuspected bony metastases. Only one patient had Looser's zones and eight patients with 'normal' or 'osteoporqtic' bone, density were shown to have histological osteomalacia. There was a strong association between steroid therapy, osteoporosis and pathological fracture, particularly in rheumatoid arthritis.