Abstract: Humoral and Cell-Mediated Immune (CMI) responses of four Angus calves following vaccination and challenge with rinderpest viruses were investigated. Both of two calves vaccinated with the rinderpest bovine ‘O` Kabete strain (RBOK) seroconverted with a mean peak percentage inhibition (PI) of 80.5 56 days post vaccination. Mean peak PI of 82 was demonstrated by sera of the vaccinated calves when challenged with the virulent rinderpest virus (RPV)-Saudi 1/81 strain 63 days post vaccination. Lymphoproliferative responses (LPR) of the peripheral blood mononuclear cells (PBMC) measured by cellular DNA {3H}thymidine uptake revealed mean peak stimulation index (SI) of 10 at day 35 of vaccination. Mean peak SI of 13.2 was attained 2 days post challenge. PBMC of the infected control calves did not respond to stimulation. The two vaccinated calves did not succumb to challenge. Based on the pattern of the responses and reaction to challenge, protection against infection seemed to be regulated by the cell-mediated immune system rather than the humoral pathway alone.