C-type particles are found in human, baboon, marmoset, rhesus, patas, and cynomolgus monkeys. A cebus monkey and two chimpanzee placentas have failed thus far to show the presence of these particles. Of the nonprimate tissues examined one mouse and one guinea pig placenta were positive whereas a rabbit placenta was negative. Variations in number of particles present in tissues as well as number of animals of a given species containing particles are noted. The isolation of foamyviruses from placenta cultures makes critical evaluation and interpretation of findings imperative. Several considerations suggest that the presence of foamyviruses is coincidental.