Monitored biclonal densities of parasites were offered to third-stage larvae of Triatoma infestans via an artificial feeding device and 30 days later, the gut contents of the insects were processed for microscopic examination and polymerase chain reaction (PCR) detection of Trypanosoma cruzi kinetoplast DNA [kDNA]). A total of 15 mixtures involving nine different stocks attributed to the 19/20, 32 and 39 major clonal genotypes of Trypanosoma cruzi were used. The presence of each T. cruzi clonal genotype after completion of the cycle through the insects was investigated by hybridising the PCR amplification products with genotype-specific minicircle kDNA probes. Sixty-five out of 90 examined insects (72.2%) were positive for parasites by microscopic examination and 85 (94.4%) were positive by PCR. The results show that almost half of the biclonal infections are not detectable after completion of the cycle, and that there are important differences in detection of such biclonal infections according to the clonal genotypes considered. Moreover, elimination of a clonal genotype by another is a frequent, but not constant, pattern in biclonal infections of T. infestans. The use of PCR and kDNA probes makes it possible to avoid the culture phase, which makes detection of mixed infections much easier in epidemiological surveys. Moreover, the fact that T. infestansdoes not transmit different T. cruzi clonal genotypes with the same efficiency has strong implications for the reliability of xenogiagnosis.