Mpk1 is the output kinase of the cell integrity cascade that includes Pkc1, Bck1, and Mkk1/2. This pathway is required for cell viability following pheromone induction. Also, the kinase activity of Mpk1 is stimulated 8-10 fold upon exposure of cells to mating pheromone. To dissect the requirements for this activation, mating pathway mutants were tested to determine where the activation signal was arising. Cells deficient in Ste12 or Ste20 were unable to stimulate Mpk1 activity. Therefore, the activation of Ste12 and presumably expression of a Ste12 dependent gene are required for the propagation of the activating signal. Consistent with this idea, cells treated with cycloheximide were unable to stimulate Mpk1 activity. We then examined the cell integrity pathway to determine the site receiving the signal. Mutants defective in Pkc1 or lacking Bck1 allowed partial activation of Mpk1 by pheromone, suggesting that there may be multiple mechanisms that contribute to the observed activation. Spa2 is known to be necessary for efficient mating, and is synthetically lethal with Bck1. Therefore, the possibility of Spa2 involvement in Mpk1 activation was tested. As predicted, mutants lacking Spa2 showed partial stimulation of Mpk1 by pheromone, but a spa2 pkc1ts double mutant was refractal to the stimulation. We propose that full activation of Mpk1 following mating pathway induction involves at least two pathways, one dependent on Pkc1 and the other on Spa2.