When potential bidders in an auction have to incur a cost to prepare their bids and thus to learn their valuations, imposing a reserve price and announcing that in case no bid is submitted there will be another auction without a reserve price is both revenue and welfare improving. Reserve prices that induce less than maximum entry in the first auction may be optimal. Also, entry fees are not necessarily better instruments than reserve prices. Journal of Economic Literature Classification Number: D44. © 1996 Academic Press, Inc.