Transgenic mice carrying the activated N-ras oncogene under the transcriptional control of the mouse mammary tumor virus (MMTV) long terminal repeat were produced. The transgene is expressed in a tissue distribution consistent with the fact that it is driven by the MMTV-LTR, and similarly to MMTV/H-ras constructs, its presence elicits tumors in Harderian, mammary and salivary glands. In addition it appears to compromise male reproductive function, which has not been described with the other ras transgenes. This finding is consistent with the existence of distinct physiological actions for each of the ras family members.