We examined the fine structural distribution of glycogen particles in the cells of the erythrocyte series from thirty individuals with or without hematological disorders using the periodic acid-thiocarbo hydrazide-silver proteinate (PA-TCH-SP) technique, which is known to extend PAS staining to the ultrastructural level. In diseases exhibiting dyserythropoiesis, such as refractory anemia with excess of blasts (RAEB) and juvenile chronic myelocytic leukemia (JCML), glycogen particles remarkably increased. In diseases showing hypererythropoiesis such as iron deficiency anemia, hemolytic anemia, or in cells obtained from very small premature infants, an increase in glycogen particles was observed in most cases. Compared to the PAS staining technique, which also utilizes the periodic acid reaction, the PA-TCH-SP technique appears to be more sensitive for visualizing glycogen particles in PAS negative cells, in addition to its capability of demonstrating the distribution of periodate reactive substance at the fine structural level.