We analysed how interactions between protein kinase-dependent intracellular signalling pathways were implicated in the control of the production of tissue-type plasminogen activator (tPA) and the generation of neurite outgrowth by PC12 cells. To that aim, cells were treated with agents that interact with the trk receptor and with protein kinases A and C. Nerve growth factor induced only the formation of large neurites. The release of the protease and the production of short neurite outgrowth were found to be protein-kinase-A-dependent events that could be enhanced by simultaneous activation of protein kinase C with phorbol ester. At high concentration, staurosporine, a nonselective inhibitor of protein kinases, induced the production of short neurites and mimicked the protein-kinase-A-dependent effect on tPA release. Such a response was not observed with K-252a, an analogue of staurosporine devoid of neurite-outgrowth-promoting activity. The responses to protein kinase A stimulation and the addition of staurosporine, although similar, seemed to occur through an activation of distinct, yet interacting, signalling pathways. In conclusion, tPA release and large neurite outgrowth from PC12 cells are controlled by parallel, albeit interacting, pathways, suggesting that these two potentially antagonistic events in PC12 cell differentiation can be modulated in a concerted way or independently of each other, depending on the activity of several protein kinases.