The objective of this study was to report the occurrence of reactivation ocular toxoplasmosis in bone marrow transplant (BMT) recipients and to propose guidelines for identification and chemoprophylaxis of high-risk patients. The study design was a series of cases from the tertiary care university hospital which has an active BMT program. The patients were two recipients of autologous BMTs with past histories of toxoplasma retinochoroiditis who developed symptomatic reactivation of ocular toxoplasmosis as documented by formal opthalmologic examination in the early post-transplant period. Opthalmoscopic examinations in the two patients with non-Hodgkin's lymphoma who received autologous transplants and then developed decreased visual acuity in the first week after transplant revealed recurrent retinochoroiditis adjacent to old toxoplasma lesions. Pre-transplant eye examinations in both patients had demonstrated only inactive chorioretinal scars. Therapy with sulfadiazine, pyrimethamine and prednisone ultimately led to resolution of retinitis in both patients. BMT recipients who are seropositive for antibody to T. gondii and have findings consistent with previous toxoplasma retinochoroiditis on pre-transplant ophthalmologic examination appear to be at risk for reactivation of ocular toxoplasmosis in the early post-transplant period and may warrant preventive chemoprophylaxis for toxoplasmosis.