Recent advances in the field of cell cycle progression have extended our knowledge of the mechanism(s) of cellular proliferation and have placed it on a solid molecular basis. This survey highlights some of these findings, selecting the most intriguing in the hope of providing new insights on cell cycle controls. We have considered two large groups of factors involved in cell cycle control: extracellular (environmental signals, ie growth factors, and their cellular receptors) and intracellular (oncogenes and anti-oncogenes), indicating which, to us, may be the most promising areas of investigation. These include the events occurring after the IGF1 receptor is activated by its ligand, the role of anti-oncogenes in preventing the activation of growth factor receptors, the mechanism(s) by which some proto-oncogenes may short circuit the cell cycle and the use of peptide analogues and the antisense strategy to study and to regulate cellular proliferation.