In the Canton of Zurich in Switzerland, 1,252 red foxes (Vulpes vulpes) were examined during 1990-1991 for intestinal stages of Echinococcus multilocularis using the mucosal smear technique. Special safety precautions were employed during examination. An average of 35% (432 foxes) were infected, mostly with low to medium numbers of gravid worms producing thick-shelled eggs. In the eleven districts of the Canton, prevalence rates varied between 13% and 57%. An average of 29% of the foxes had antibodies in serum or body fluid against a highly species-specific antigen of E. multilocularis (Em2-antigen). The fact that foxes with intestinal E. multilocularis infection have been found in all parts of the Canton of Zurich indicates a relatively high potential infection risk for humans, but apparently the risk is reduced by certain extrinsic or intrinsic factors which have yet to be determined.