Chromosomal in situ hybridization with radioactive probes allows the detection of small chromosomal rearrangement which were undetectable with other cytogenetic methods. In two species of Lemurien; Microcebus murinus and Eulemur fulvus, the banding patterns of Microcebus murinus chromosome 3 and Eulemur fulvus chromosome 2 demonstrates very similar ones, excepting position of centromeres. In situ hybridization with beta-nerve growth factor probes on the chromosomal preparations of these two species detected intra-chromosomal pericentric inversion during chromosomal evolution.