The production of ascitic fluid and splenomegaly on intraperitoneal injection in weanlings was used as a test for microsporidia after introduction by other routes and in other loci. Oral and cerebral administration was followed only by enlarged spleens which reproduced the ascitic response on passage. Microsporidia were demonstrable by phase microscopy in all fluids. Positive findings were also obtained with liver, kidney, brain, lungs, blood, and urine. Intramuscular and intranasal injection were occasionally followed by ascites, but splenomegaly again predominated. The results of contact experiments indicated that the organisms were not readily communicable either in weanlings or nurslings. Relation of the microsporidian to Encephalitozoon cuniculi (Nosema cuniculi Lainson et al.) is discussed.