The aim of this review has been to present our view of the interaction of functionally distinct T cellsubsets involved in the generation of cytotoxic T cell respinses. The preactivation of CTL-P is induced bycomplex antigens, most frequently composites of viral and self- MHC class I(H-2) histocompaitbility antigens.The clonal expansion (growth) and differentiation into lytic effector cell is mediated by the CTL-class-specific lymphokines II-2 and CTDF, respectively. The II-2 producer cell is Lyt-1+ T helper cell which, byvirtue of its lymphokine secretion, tightly controls the CTL activation. Under conditions where the growthand diffrentiation-inducing lymphokines are supplied in excess, the frequency of antigen-inducible CTL-Ps orCon A-responsible CTL-Ps (total pool) can be enumerated directly. Thus, the repertoire of CTL-Ps in variouslymphocyte population is now amenable to quantitative studies at a clonal level. Furthermore, since largequantities of biochemically defined lymphokines such as II-2 may soon become available, the prospect ofanalysing the immunoregulatory effect of this growth factor under pathophysiogical conditions (with a potentialtherapeutic interest) mightsoon be realized.