EXHIBIT 4 August 4, 1997 Dear Stockholder: By now you should have received the Offer to Purchase dated July 29, 1997 relating to the offer (the "Offer") of NPB Acquisition Corp., a Delaware corporation ("Merger Sub") and wholly-owned subsidiary of...Offer to Purchase • August 5th, 1997 • Nellcor Puritan Bennett Inc • Electromedical & electrotherapeutic apparatus
