The IUCN Red List of Threatened Species is often advocated as a tool to assist decision-making in conservation investment and research focus. It is frequently suggested that research efforts should prioritize species in higher threat categories and those that are Data Deficient (DD). We assessed the linkage between IUCN listing and research effort in DD and Critically Endangered (CR) species, two groups generally advocated as research priorities. The analysis of the change in the research output following species classification indicated a listing effect in DD species, while such effect was observed in only a minority of CR species groups. DD species, while chronically understudied, seem to be recognized as research priorities, while research effort for endangered species appears to be driven by various factors other than the IUCN listing. Optimized conservation research focus would require international science planning efforts, harmonized through international mechanisms and promoted by financial and other incentives.