SummaryA viral agent, PR10, isolated from a Puerto Rican infant with gastroenteritis has been designated as the prototype strain of ECHO-32 by the Panel for Picorna-viruses (3). ECHO-3 2 (1) produced entero-virus-like CPE in rhesus monkey kidney tissue cultures, (2) bore no antigenic relationship to known enteroviruses, (3) produced no disease in the common laboratory animals or embryonated eggs, (4) was insensitive to desoxycholate or ether, (5) was stabilized by M MgCl2 to heating at 50°C for one hour, (6) demonstrated a red staining reaction with acridine orange indicating an RNA core, and (7) was estimated to be 26-27 mμ in size.We are indebted to Col. A. C. Sanders for his encouragement and support, to Dr. C. Mattern for the electron micrograph, to Dr. H. A. Wenner for supplying candidate virus strains, to Col. H. Sprinz for the monkey autopsy report, and to Dr. E. H. Lennette for sending us the modified plaque method.