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Exploratory laboratory, greenhouse, and field experiments in 1961 and 1962 were used to study the cobalt (Co) nutrition of soybeans in Indiana. The Co treatments were applied by either seed or foliar methods. Co treatments greater than 36.8 mg/kg of seed applied to the seed as the sulfate salt produced chlorosis of the leaves and stunted the young seedlings. Mild chlorosis could be completely corrected by adding Fe salts. A three-state survey conducted in Illinois, Iowa, and Indiana (1961) reported similar results with CoSO₄ seed treatment at the rate of 92 mg/kg seed. Between 48 and 65% of the 396 fields studied reported the development of chlorotic seedlings. A controlled field experiment conducted in 1961 showed only decreased yields from Co applied at the rate of 184 mg/kg seed, but a similar experiment conducted in 1962 with Co applied at the rate of 18.4 mg/kg showed increased yields in three of the five locations. However, none of these differences in the latter two tests were significant at the 5% level. In a later study direct evidence for the translocation of foliar applied Co to the nodules was obtained using Co