This study showed several accumulated data through ten years from our experience in hematopoietic disorders and associated infections, which has been analyzed by the Hanshin Study Group of Hematopoietic Disorders and Infections. Since 1979 to 1988, our group had evaluated the sorts of causative organisms and the efficacy of various antibiotics therapy in 2119 cases of infectious diseases associated with hematopoietic disorders. On behalf of evaluating the changes of disease profile for ten years, we divided the accumulated data into three phases; former phase the first three years, middle phase the second three years and late phase the last four years. There was no significant difference in the frequency of various hematopoietic disorders among the three phases. Each leukemia patients occupied 77% of all cases. Sepsis suspected is the most frequent infectious disease accounting for 68.8%. The other infectious diseases were 8.4% of the sepsis, 14.8% of the respiratory infections and 3.1% of the urinary tract infections. Comparing the frequency of infections among the three phases, the respiratory and urinary tract infections inclined to decrease. Of the 532 strains isolated from 2119 cases and identified as causative organisms, gram-negative bacilli occupied 62.8% and gram-positive bacteria 36.5%. In comparing the percentage of gram-negative bacilli among the three phases, it showed a decreasing tendency in order former phase 63.6%, middle phase 76.4% and late phase 43.8%. Pseudomonas, however, had been isolated at almost constant ratio through ten years. On the other hand, the ratio of gram-positive bacteria isolated were 34.5% in former phase, 23.6% in middle phase and 56.3% in late phase, showing increasing a tendency through the period. Twenty-three kinds of antibiotics were administered by intravenous drip infusion. The efficacy rate was 43.9% to 67.2%. In particular, effectiveness of antibiotic therapy often depends on the change of peripheral neutrophil counts from the onset and during the therapy. The efficacy rate, however, was 36% even neutrophil counts have not shown the tendency of increase from less than 100/microliters.