Further to an epidemiological survey carried out in cattle, in 1991-92, epidemiological surveillance in cattle and complementary survey in sheep were carried out between 1993 and 1996, with parasitological and serological techniques (indirect-ELISA T. vivax). In sheep, 163 samples were collected in 1991-93, all were negative; 164 samples were collected in 1994, showing that the infection by T. vivax occured inapparently in some cases, and with drastic symptoms induding abortion in others; the parasite was observed in one farm only. In cattle, 495 samples were collected in 1992-94, the parasite was not observed but the mean seroprevalence was of 7.8 16. 183 samples were collected in 1994-95, during an outbreack of trypanosomiasis, the parasite was observed in 7 of the 8 farms investigated, with a mean seroprevalence of 50%. 863 samples were collected in 1995-96, the parasite was observed in a single animal amongst 309 samples from one farm, in the absence of symptoms, and numerous animals in an outbreak in imported cattle; the mean semprevalence during that period was about 26 16. It was observed that sheep and cattle can be infected with or without symptoms, depending on the zootechnic level of the farm, espedally water and food supply. Incidence above 70% were observed whidhever period of the year, even when the abundance of tabanids is at its lower level; crepuscular tabanids of the genus Chlomtabanus were suspected to be vector of the disease. Self cure was observed in cattle at a mean rate of15-20% a year, inapparent circulation of the parasite was observed in a cattle farm with a satisfying zootechnic level at a rate of 2% a month. Acting as reservoir, sheep may have an important role in the epidemiology of T. vivax in cattle. Trypanosomiasis due to T. vivax is a permanent threat for cattle and sheep breeding in French Guyana.