Dexamethasone increases BFU-E colony formation, whereas lenalidomide increases CFU-E colony formation, and the combination of drugs is additive. After 3 days of treatment with the compounds in liquid culture, cells were plated in methylcellulose without drugs. Data are presented as the number of colonies per 3200 cells plated. The effects of dexamethasone (Dex) are shown in panel A and the response to lenalidomide (Len) is shown in panel B. The effects of combinations of Dex and Len on CFU-E are shown in panel C and the effects on BFU-E in panel D. The expected number of colonies was calculated as follows: expected number of colonies = (Dex-alone colonies − control) + (Len-alone colonies − control) + control. The experiments were performed in triplicate and repeated with similar results. In panels A and B, a 2-tailed Student t test was used. **P ≤ .01; *P ≤ .05. In panels C and D, ANOVA was used and the statistical findings are discussed in the text.