A summary review of leukocyte function in 42 published cases of glycogen storage disease Ib is presented. Polymorphonuclear and monocyte dysfunctions were evidenced in the majority of cases, whereas lymphocytes appeared to be unaffected. Phagocyte dysfunctions comprised in vivo mobilization and motility, in vitro random and directed migration, and one or several component functions of the “metabolic” (“respiratory”) burst. On the basis of the available data it is impossible to know whether a primary functional deficit of the glucose 6-phosphate transport protein of the microsomal glucose 6-phosphatase system, as demonstrated in liver, also exists in these phagocytic cells and is responsible for this dysfunction.