Exhibit 21.1 SUBSIDIARY STATE OF INCORPORATION D/B/A - ---------- ---------------------- ----- ESI Canada, Inc. New Brunswick, Canada None ESI Canada Holdings, Inc. New Brunswick, Canada None Express Scripts Vision Corporation Delaware ESI Vision Care IVTx, Inc. Delaware None IVTx of Dallas, Inc Texas None IVTx of Houston, Inc. Texas None Great Plains Reinsurance Company Arizona None PhyNet, Inc. Delaware None Practice Patterns Science, Inc. Delaware None