The U.S. Postal Service’s Computerized Delivery Sequence (CDS) file is widely used as the sampling frame for household surveys conducted by face-to-face interviewing. However, the file suffers from some undercoverage for such surveys, partly because unlocatable addresses have to be dropped from the frame. This paper describes the Address Coverage Enhancement (ACE) procedure that aims to supplement the CDS file to deal with the undercoverage, and assesses its strengths and challenges. One of its strengths is that it is applied in only a subsample of the sampled segments. Another strength is that it retains addresses sampled from the CDS file that are erroneously geocoded to a sampled segment. However, as a result, addresses added through the ACE procedure have to be compared to the CDS file to determine if they are elsewhere on the file. This task has sometimes proved time consuming. A feature of the ACE procedure is that methods need to be developed to assign selection probabilities for subsampling the segments in which the procedure is applied.