Interest in retinoic acid, the main biologically active derivative of vi- min A or retinol, increased dramatically between 1989 and 1993, following the cloning of nuclear receptors or RARs reported in 1987 (Fig. 1). Important discoveries since then have shown how RARs work as all-trans retinoic ac- dependent heterodimers with related nuclear receptors for 9-cis retinoic acid called RXRs. This has stimulated the development of synthetic analogs s- cific for each type of receptor, and opens the way to develop new methods for regulating pharmacologically the activity ofretinoic acid-dependent pathways of gene activation. The potential for the development of new drugs by the pharmaceutical industry is now a maj or factor driving forward our understa- ing of vitamin A-regulated pathways in animal development and homeostasis. However, apart from the real potential ofretinoid analogs as novel pharma- logical agents, there remains the considerable intellectual challenge of und- standing the way in which vitamin A and its derivatives function in cell development and differentiation. Retinoid Protocols is an attempt to bring together various methodologies that will be vital for rising to this challenge in the future. Retinoid molecular biology has few methods of its own, but is reliant on standard molecular biology methods applied to this particular research area.