Monitoring the moisture content of lumber is an important part of the manufacturing process. Lumber that is too wet or too dry will have a lower value than properly dried lumber. The cumulative sum (CUSUM) chart is proposed as an alternative to traditional control charts for detecting small sustained changes in the mean charge moisture content of kiln-dried lumber. Charts are presented and interpreted for two kilns. The CUSUM chart readily detected changes in the mean moisture content that were not detected with an X-chart. For the CUSUM chart to work well, the process must be in a good state of control with the mill’s average moisture content near the target moisture content.