T. vivax DNA detection polymerase chain reaction (PCR) appears to be an alternative for a species-specific diagnosis of T. vivax active infections in livestock. PCR highly sensitive when processed on purified DNA from DNA extraction with ethanol/chloroform, but this technique is too expensive and time-consuming to be applied for diagnosis. First evaluation of the PCR directly applied for the diagnosis of T. vivax in cattle indicated a low sensitivity about 10(3) parasites/ml. Sensitivity of several techniques of low cost were evaluated with determined parasitaemia. 22 blood samples containing known numbers of T. vivax/ml, were prepared by dilution of infected sheep blood into blood from a non infected sheep. Sensivity of the PCR was evaluated in the following blood sample preparations: heparinized blood, plasma, lysed blood, burly coat from haematocrit capillary tubes, pellet from plasma centrifugation, and DNA purified with a commercial ion exchange resin. Most often, crude heparinized blood inhibited the PCR. Sensitivity of PCR with plasma and lysed blood was low, around 450 parasites/ml. PCR on buffy coat was more sensitive, but products were sometimes hardly visible. Pellet of plasma centrifugation an original, fast and economic preparation, which presented a high sensity: 100% of the samples were positive when the parasitaemia was over 13 parasites/ml. DNA purification is slightly more time-consuming and expensive, since it procedes from several manipulations and the use of a kit, but it appeared to be the most sensitive technique among those investigated