A selection experiment in barley was performed to determine whether worthwhile increases in yield could be obtained by selecting among F4 families for the morphological components of grain yield. The data were used as a basis for examining relationships among yield and its components. Selection for number of heads resulted in changes in yield that were similar to those observed when selection was for yield itself. Selection for kernel weight was highly effective in altering yield in one of two populations. In contrast, yield was reduced in one population when selection was practiced for kernels per head. Thus, selection for yield through components was very effective in certain situations, but could not be recommended as a routine procedure. Genetic as well as environmental factors were responsible for the observed phenotypic correlations between the components of yield. These phenotypic correlations were unreliable as an indicator of the yield responses that occurred when selection was practiced for the components of yield. It was postulated that the optimum genotypic level for kernels per head and number of heads will vary depending on environment, but that the optimum. for kernel weight will be near its genetic maximum