The early region of the cottontail rabbit papillomavirus (CRPV) genome has been introduced into a retroviral vector and recombinant retroviruses, produced upon transfection of the psi 2 packaging cell line, have been used to infect NIH 3T3 cells. Spliced derivatives of the CRPV early region can be rescued from the infected cells. Sequence analysis demonstrates that the major splicing event observed in RNA in tumours is faithfully reproduced in this system. This splice generates a polycistronic mRNA that contains in its 5' portion the E7 open reading frame, or both E6 and E7, and at its 3' end a reading frame with codons for three amino acids from the N-terminus of E1 linked to codons for 100 amino acids from the C-terminus of the E4 region. Recombinant retroviruses containing intact or spliced CRPV sequences can now be used to introduce the viral genes efficiently into a variety of cell lines.