Tritrichomonas foetus has three anterior flagella and one recurrent flagellum. The latter originate at the anterior portion of the protozoa and extends towards the posterior region of the cell adhering to the cell body. Freeze-fracturing studies showed in the flagellar membranes of the three anterior flagella, groups of nine to 12 intramembrane particles forming rosettes which could be observed on both the P- and the E-faces of the flagellar membrane. The rosettes are numerous and found along the length of the flagella. No such structure was seen in the membrane of the recurrent flagellum. The rosettes coexist with other particles in apparently random distribution.