RNA-binding proteins can strongly regulate and influence the cellular function and fate of an RNA molecule. Of the many described nucleic acid-binding domains, the double-stranded RNA-binding domain (dsRBD) is a highly specialized example found in a wide variety of proteins with diverse cellular functions. Mostly present in multiple copies and highly homologous to one another, the individual functional specificity of dsRBDs is now becoming apparent. Here we review recent evidence showing that single dsRBDs within individual proteins are capable of distinct in vivo functions. Not only does this enable dsRBD-containing proteins to increase their functional diversity but it also reveals novel and unexpected roles that dsRBDs can perform. (C) 2002 Elsevier Science (USA). All rights reserved.