Diagnosis of Trypanosoma equiperdum, the causative organism of dourine in horses, by standard parasitological techniques is difficult, owing to the low numbers of parasites present in blood or tissue fluids and the frequent absence of clinical signs of disease. Consequently, the demonstration of trypanosomal antibodies in the serum has become the most important parameter in determining the disease status of individual animals and serological testing by the complement fixation test (CFT) is widely used in the health certification of horses for export (Wassal et al., 1991). Although the CFT has been in use many years for diagnosis of dourine it is considered to be less sensitive than enzyme-linked immunosorbent assays (ELISAs) and it has been suggested that ELISAs could replace the CFT for health certification purposes (Caporale et al., 1981; Wassail et al., 1991). Indeed, it is the intention of the Central Veterinm T Laborato D, (CVL) of the United Kingdom Ministry of Agriculture that enzyme immunoassays should be adopted in investigations of a number of haemoprotozoan diseases of horses in order to limit the number of test systems employed in the diagnosis of infection. The present work was undertaken to investigate the applicability of ELISAs for the detection of antibodies and antigens using reagents which are more critically defined that those that have so far been employed in the diagnosis of infections with dourine.