Groups of 20 lambs were vaccinated with parainfluenza virus type 3 PI3by the intranasal (I.N.) or intramuscular route (I.M.).Approximately 6 weeks later, vaccinated and non-vaccinated lambs were challenged sequentially with PL3, andPasteurella haemolytica. At slaughter, 10 to 12 days after challenge, 65% of non-vaccinates and 45% of I.M. vaccinates had pneumonic lesions whereas lesions were not observed in any of the I.N. vaccinates.