Treatment of dividing plant cells with caffeine inhibits their cytokinesis, thereby inducing the formation of binucleate cells that contain polyploid nuclei. This study was undertaken to determine whether caffeine treatments would induce chromosome doubling and seed set in haploids of common wheat (Triticum aestivum L. em. Thell.) through the further development of diploid nuclei. Ten sterile wheat haploid plants, obtained through the agency of corn (Zea mays L.) pollination, were multiplied by vegetative propagation (subdivision of well-tillered plants) to produce about 50 crowns per haploid. Washed and trimmed crowns were treated with 0.3, 1.0, 3.0, and 10.0 g∙L−1 caffeine for 3, 6, 12, and 24 h. While treatment with 0.3 g∙L−1 caffeine did not restore fertility, higher concentrations of caffeine resulted in pollen shedding and substantial seed set compared with untreated controls. Many combinations of caffeine concentration and duration produced comparable results; however, treatment with 3 g∙L−1 for 24 h was the most effective caffeine treatment on the basis of the number of seeds recovered, as well as the size and incidence of fertile sectors. Compared with a standard colchicine treatment (3-h immersion in 2 g∙L−1 colchicine dissolved in 0.5% dimethyl sulfoxide), all caffeine treatments produced fewer seeds, principally because colchicine-doubled sectors were often large, while caffeine-doubled sectors were numerous but generally small. In conclusion, caffeine produced useful numbers of seeds for all clones; gliadin banding patterns and chromosome counts indicated that genetic and cytogenetic stability of the doubling process were equal or superior for caffeine compared with colchicine.Key words: chromosome doubling, haploid, caffeine, colchicine, Triticum aestivum.