Reovirus-like particles have been identified in stools of children with diarrhea by using several different methods of preparing the stools for EM, and incidences of the reovirus-like agent in groups of patients with diarrhea have been reported. Since no standardized stool processing method was used, it is difficult to compare the incidence figures published. This study evaluates 2 commonly used methods to determine which is more sensitive for use in future clinical studies. Stool samples from 72 Mexican children who had acute-onset diarrhea were processed for reading by EM by the pseudoreplica technique and by differential centrifugation. Reovirus-like particles were seen in 25 samples (34.7%) when the results of both methods were combined. With the pseudoreplica technique 22 samples (30.6%) contained the viral particles; with differential centrifugation 21 (29.2%) had particles. The 2 methods are equally reliable for demonstrating reovirus-like particles in stool samples. The pseudoreplica technique, which is quicker and less expensive than differential centrifugation, is the preferred method for clinical studies of diarrhea associated with reovirus-like particles.