Results of a field experiment comprising soil application of elemental sulfur, ferrous sulfate, and gypsum, along with a control and foliar sprays of 0.1 percent H2SO4, FeSO4, sequestrene 138-Fe, MnSO4, and ZnSO4along with no spray showed that soil application of 250 kg/ha of elemental sulfur and foliar sprays of H2SO4and FeSO4increased cowpea yields by 38.0, 32.6, and 33.4 percent, respectively. The increase in grain yield of cowpea was associated with the increase in leaf contents of sulfur, nitrogen, and a, b, and total chlorophyll. Soil application of gypsum or FeSO4was only 82 percent as effective as elemental sulfur. The results show that chlorosis in cowpea does not represent any deficiency of iron or other micronutrient, and that it is on account of low supply of active sulfur. Since yield increases with soil application of elemental sulfur and foliage application of 0.1 percent H2SO4or FeSO4are of the same magnitude, an application of H2SO4is recommended to prevent chlorosis and increase crop yield of cowpea as the treatment is almost costless. The beneficial results of FeSO4, MnSO4, ZnSO4, etc., reported in the past seem to be on account of inadvertent supply of sulfur and/or low pH of salt solutions which jointly increase physiological availability of iron at the site of biosynthesis of chlorophyll.