The polymerase chain reaction has all attributes of a promising diagnostic technique. It is rapid, simple to perform and extremely sensitive. In a PCR developed for the detection of small ruminant lentiviruses (SRLV), we found under ideal conditions a detection on sensitivity up to less than 10 template DNA copies. The diagnostic application of PCR was not fully satisfying, even when the technique was refined by the use of a panel of suitable primer pairs. The reliability of PCR in blood and milk samples was much lower than that of antibody detection using ELISA. Interestingly, a positive PCR result was also recorded in 50% of the samples of seronegative animals. Seronegative lentivirus carriers due to delayed seroconversion have been described previously (Rimstad et al., 1993). Due to sporadic occurrence of false positive reactions in spite of contamination control, this result must be interpreted with caution unless the specificity of the fragments can be confirmed by sequencing. Using published sequences of SRLV, we show that sequencing of PCR products, followed by phylogenetic analysis should allow to study molecular epidemiology of field strains.