EXHIBIT 21 SUBSIDIARIES OF THE REGISTRANT Status as of Name Incorporation December 31, 1997 - -------------------------- ------------- ----------------- Wisconsin Public Service Corporation (1) Wisconsin Active WPS Leasing, Inc. (2) Wisconsin Active WPS Energy Services, Inc. (1) Wisconsin Active WPS Power Development, Inc. (1) Wisconsin Active WPS Visions, Inc. (1) Wisconsin Active PDI Operations, Inc. (3) Wisconsin Active PDI Stoneman, Inc. (4) Wisconsin Active - ---------------- (1) Wholly-owned subsidiary of WPS Resources Corporation. (2) WPS Leasing, Inc. is a wholly-owned subsidiary of Wisconsin Public Service Corporation. (3) PDI Operations, Inc. (formerly known as PDI Stoneman Operations, Inc.) is a wholly-owned subsidiary of WPS Power Development, Inc. (4) PDI Stoneman, Inc. is a wholly-owned subsidiary of WPS Power Development, Inc. -249-