Technical Abstract: The Agricultural Research Service, United States Department of Agriculture announces the release of seven breeding lines of crisphead lettuce (Lactuca sativa L.) with resistances to corky root and lettuce mosaic, 04-0344, 04-0350, 04-0353, 04-0363, 04-0368, 04-0375, and 04-0379. The lines may be suitable for commercial production, and is suitable for use as a source of resistance to corky root and lettuce mosaic in the development of cultivars and germplasm. It was developed at the United States Agricultural Research Station in Salinas, California by Beiquan Mou, Ryan J. Hayes, and Edward J. Ryder. Corky root of lettuce (Lactuca sativa L.) has been observed in major lettuce-producing areas of the world, and yield losses from reduced head size can reach 30-70%. Lettuce mosaic is a serious virus disease problem in lettuce worldwide and can cause losses of up to 100%. The breeding lines were derived from crosses between cultivars ‘Salinas 88’, and ‘Glacier’ and ‘Misty Day’, which have resistant genes to corky root and lettuce mosaic. In multiple lab and field tests, the breeding lines showed high levels of resistance to the two diseases. In the limited trials grown, the breeding lines have performed well in the Salinas Valley, Calif., produce a high percentage of heads of adequate size, shape, and uniformity. Limited samples of seed are available for distribution to all interested parties for research purposes, including the development and commercialization of new cultivars. Samples will also be deposited in the National Plant Germplasm System.