Several hundred smelt died during an epidemic at Loon Pond, Gilmanton, N. H. The causative organism was identified as Glugea hertwigi. Cysts covered the greatly distended intestine and were also found in the pyloric caeca and on occasion in the heart, liver, and gonads. The intestine appeared to be the primary site of the infection; the lumen being partially or completely occluded. About 30% of the smelt were infected with Leptorhynchoides thecatus. G. hertwigi has also been found in marine O. mordax from the brackish waters of the Oyster River at Durham, N. H.