A lead-in guide assembly is shown for centralizing a downhole tool being run from a well surface within a well bore to a selected downhole location. The lead-in guide can be utilized as a seal assembly guide including a seal carrier provided with a leading end and a trailing end which is made up in a tubing string leading to the well surface. A collapsible guide is located at the leading end of the seal carrier for centralizing the seal carrier within the surrounding cased well bore as the seal assembly is being run into position above a cooperating sealing bore located at a downhole location. The guide means moves to a retracted position as the assembly moves within the cooperating sealing bore.