Intra-testicular inoculation of an adenoviral vector carrying the fusion gene Aequorea victoria green fluorescence protein/rat-liver glycogen synthase (GFP/LGS) resulted in the presence of GFP/GLS in spermatozoa from 7 days to, at least, 16 days after inoculation. The GFP/LGS was detected in the sperm heads after an "in vitro" fertilization procedure, either before or after the oocyte penetration. Out-results indicate that spermatozoa carrying GFP/LGS protein conserved their fertilizing ability and were also detectable after oocyte penetration. This technique will allow to develop an easy system to follow the fate of mature sperm proteins. (C) 2002 Elsevier Science (USA). All rights reserved.