The authors give a short overview on:--Diseases characterized by too small a number of osteoblasts and insufficient osteoid formation--Bone diseases in the presence of osteoid overproduction with concomittant disturbed mineralization can quasi be summed up in two statements as regards ageing and aged people--Diseases associated with excessive resorption due to increased osteoclastic activity--Diseases caused by great resorption of bone in the presence of bone marrow proliferation, their diagnostics, prophylaxis and therapy.