A plasmid containing a full-length cDNA copy of the Lelystad virus isolate (LV) of porcine reproductive and respiratory syndrome virus was constructed. When RNA that was transcribed in vitro from this full-length cDNA clone was transfected to BHK-21 cells, infectious LV was produced and secreted. The virus was rescued by passage to porcine alveolar lung macrophages or CL2621 cells. When infectious transcripts were transfected to porcine alveolar lung macrophages or CL2621 cells no infectious virus was produced due to the poor transfection efficiency of these cells. The growth properties of the viruses produced by BHK-21 cells transfected with infectious transcripts of LV cDNA resembled the growth properties of the parental virus from which the cDNA was derived. The infectious clone of LV enables us to mutagenize the viral genome at specific sites and thus will be useful for detailed molecular characterization of the virus, as well as for the development of a safe and effective live vaccine for use in pigs.