Adoption of the improved maize package was particularly rapid during the period 1980-86 when an attractive guaranteed price was offered and extension activities were reinforced by a maize project that included the establishment of a seed multiplication program. Following cereal market price liberalization in 1986, maize prices fell and have been subject to considerable variability. Area has continued to expand, but farmers have greatly reduced fertilizer use, switched back to maize-late millet intercropping, and substituted early maturing varieties better suited to their own food security needs. The estimated internal rate of return (IRR) to investment in maize research and extension in southern Mali over the period 1969-90 is 135%. This high rate can be attributed to low research costs (much of the technical package was borrowed from research conducted elsewhere in West Africa), and the high economic value of maize as an import substitute. Sensitivity analysis indicates that the IRR is robust with respect to adverse changes in assumptions concerning overvaluation of the exchange rate, research costs, extension costs, and area of improved maize. It is moderately sensitive to price and yield reductions.