By 1989, bone marrow transplantation had become an effective and accepted treatment for an increasing number of diseases of the bone marrow and the immune system. Until only a few years prior to 1989, most marrow donors were siblings, carefully matched for HLA (tissue) antigens. Since only a small proportion of candidates for a bone marrow transplant have matched brothers or sisters, additional family members were tried as donors. These included parents, children, slightly mismatched siblings, and other relatives. Even with the broadening of the bone marrow donor source, no more than 30-40 percent of patients with diseases amenable to marrow transplant therapy had available donors. Improved results with these selectively mismatched relatives and a distinct need to provide appropriate treatment for more patients led to trials with unrelated, HLA-matched community volunteers as bone marrow donors. By 1989, research had progressed to the point where transplants from such unrelated donors were nearly as successful as those from matched siblings, when stratified by disease status and risk parameters. In 1989, 20 to 25 percent of patients for whom a formal donor search was initiated received a transplant. This was expected to increase substantially.