Using information on time costs of training and gains in wages attributable to training, rates of return on training investments were compared. The range of estimates based on several data sets generally exceeds the magnitude of rates of return usually observed for schooling investments. It is not clear, however, that the difference represents underinvestment in job training. Two methods were used to estimate total annual costs of job training in the U.S. economy for 1958, 1976, and 1987. The "direct" calculation uses information on time spent in training and on wages. For 1976, costs so calculated amounted to 11.2 percent of Total Employment Compensation, which is about half of the costs of school education. In the "indirect" method, training costs were estimated from wage functions fitted to Michigan's Panel Study of Income Dynamics data. In 1976 the direct estimate amounted to between 65 percent and 80 percent of the indirect estimate based on the wage profile. The result provides strong support for the human capital interpretation of wage profiles. The estimates indicate a slower growth of training than of school expenditures in the past decades. Substitution of schooling for job training is a likely cause. (Twenty-eight references and five tables are included.) (Author/NLA)