Bradyzoites of Toxoplasma gondii survived in pepsin solutions and in trypsin solutions. After 120 minutes in trypsin solution at 37 C, infectivity of bradyzoites for mice was reduced 100-fold, whereas in pepsin solution there was no reduction in infectivity. Tachyzoites survived in trypsin, but after 15 and 60 minutes' incubation at 37 C, there was a 100,000-fold reduction in infectivity titer. Toxoplasma gondii was demonstrated in mice inoculated with experimentally infected goat brain digested in pepsin and in trypsin solutions, but not in mice inoculated with undigested brain of the same goat. Seemingly, tissues should be digested in pepsin solution to isolate T gondii from chronically infected animals.