Grubs ofAtaenius spretulusHarold, a scarabaeid turf pest, were encountered at 2 widely separated locations in New York during 1969–71. All field-collected grubs were infected with a bacillus producing a milky disease similar to that produced byBacillus popilliaeDutky orB. lentimorbusDutky in other scarabaeid grubs. This bacillus was noninfective to grubs of the Japanese beetle,Popillia japonicaNewman, and northern masked chafer,Cyclocephala borealisArrow, and only mildly infective to the European chafer,Amphimallon majalis(Razoumowsky).Histological examination of infectedAtaeniusgrubs indicated that sporulation occurred in connective tissue sheaths and possibly also in lobes of the fat-body.Cytological studies showed the general ultrastructure of the spore to be similar to those reported for the other milky disease bacteria. It differed in the smallness of the endospore relative to the size of the whole sporangium, the greater number of ridges formed by the spore coat, and the presence of conspicuous exosporium. The results of our investigations suggest that the etiological agent of theA. spretulusdisease is a new milky disease organism.