Specific Giardia lamblia probes were used in order to differentiate isolates of Giardia lamblia. Analysis of DNA restricted with 2 endonucleases and 2 different probes was able to distinguish 3 different patterns of banding from 6 isolates of G. lamblia. This technique can be used to identify isolates and would be useful in epidemeology studies. Giardia specific probes were developed and used to detect minute quantities of DNA present in small numbers of organisms in hopes of developing an assay for Giardia specific DNA in stool. Although 500 cultured organism of less could be detected on nitrocvellulose, when mixed with stool the sensitivity of the assay was greatly decreased.