Superfund (CERCLA) legislation requires the Agency for Toxic Substances and Disease Registry (ATSDR) and EPA to prepare a list of at least 100 hazardous substances most commonly found at National Priority List sites or facilities that pose the most significant potential threat to human health (52 FR 12866, April 17, 1987). CERCLA also requires the agencies to revise the priority list to include 100 or more additional hazardous substances (53 FR 41280, 10/20/88) and to include at least 25 additional substances in each of the three successive years following the 1988 revision (54 FR 43615). This notice contains the required list of 25 additional substances and provides a summary of the procedure used to generate this list. For further information contact the Division of Toxicology, ATSDR, Atlanta, FTS 236- 6000 or 404-639-6000.