 Plaa's primary area of research was hepatotoxicity, in which his successes where achieved primarily by the investigation of mechanistic toxicology.His primary contributions were in the areas of cholestasis and toxic potentiation, in particular potentiation by haloalkanes.Although the use of the isolated perfused liver was already well-known, having been first used in the early 19th century, Plaa was the first to use it for the study of hepatotoxicity.