One of the major problems in studying Giardia cysts is separating this form of the parasite from faecal debris and bacteria. We approached this problem by passing filtered stool suspensions over a column of Sephadex G-50 followed by low speed centrifugations. The Sephadex retained most of the faecal debris and the centrifugation reduced the bacterial flora more than 10(5)-fold to less than 3 X 10(4)/ml. Cyst recovery was 61% (+/- 28%). This new method of separating G. lamblia from faecal material is simple, rapid, and effective.