We have identified 41 novel and many previously known growth response genes induced in regenerating liver and insulin-treated Reuber H35 cells, a rat hepatoma cell line that grows in response to physiologic concentrations of insulin and retains some properties of regenerating liver. Although many genes are expressed similarly in the two systems, there are important differences in the kinetics of induction of some genes. These differences allowed us to identify and characterize novel genes that are highly insulin-induced and expressed as delayed-early genes in regenerating liver. Sequence analysis of CL-6, the most abundant insulin-induced gene, resulted in the identification of a highly hydrophobic hepatic protein. Sequence analysis of HRS, a highly insulin-induced delayed-early gene, demonstrated that it is a member of the family of regulators of alternative pre-mRNA splicing. Different forms of HRS mRNA are temporally regulated during the growth response, suggesting that HRS could autoregulate processing of its pre-mRNA. Given the dramatic increase in RNA production during late G1, proteins induced by mitogens like insulin that control RNA processing are likely to have important roles in cell cycle regulation.