TMgeneDB is a collection of genes and sequence elements from algae and protozoa that are associated with toxic metal metabolism. The genes and sequence elements are classified into four functional categories: sensing, transport, binding, and transformation. The current release includes 1,288 toxic metal–related genes and sequence elements involved in the bioremediation of mercury (Hg) and cadmium (Cd). The database supports online searches by gene identifier, functional annotation, toxic metal element, and species name.