Frozen sections of Schistosoma mansoni adults and cercariae were prepared for use as slide antigens in the indirect immunofluorescence test for schistosomiasis. Unfixed adults embedded in Tissue-Tek O.C.T. medium for frozen sectioning gave the best combination of sensitivity and specificity. Cercarial antigens reacted intensely with Trichinella anti-sera. Extensive evaluation of the frozen S. mansoni and S. haematobium adult antigens indicated that the sensitivities were 91.7% and 85.4%, respectively; specificities were 95.8% and 96.9%, respectively. Within-run reproducibility within one twofold dilution was 93.7% and 97.9%, respectively. Determination of infecting species by serology was not possible.