A report is given of a quantitative analysis of some histological parameters in the middle frontal gyrus of the human cerebral cortex. The postnatal development of the nerve cell body volume in layer III and V shows from birth to 24 months of age two periods of growth separated by an interphase. The interphase for the pyramids in layer V occurs at about one month and for the pyramids in layer III at about two months. Already at birth the definite features of packing density are established. Layer IV is characterized by the highest packing density and layer V by the lowest. The gray cell coefficient is lower in layer V and shows an almost twofold increase from birth to adulthood in layer V and III, but a nearly fivefold increase in layer IV. Chromophil granules, clumps and true Nissl bodies increase in quantity in the cytoplasm of neurons in the cortex from about three months to two years of age. Analysis of the basal dendrites of the pyramidal cells has shown a number of characteristic features: (a) The mode of distribution of the intersections of the dendrites and the changes in the dendritic field from any one of the cortical pyramids is quite similar, whether found in layer III, IV or V. (b) The histograms illustrating the mode of distribution show rather sharp modal values, (c) Temporal rather than spatial differences were observed in the development to the dendritic plexus of the various neurons. Stellate cells show similar changes in regard to the development of the dendritic plexus. From newborn to adulthood an exponential relationship of dendritic density and distance from the perikaryon exists in the pyramids of layer III, IV and V. The size of the regression coefficient was shown to be a measure for the expansion of the dendritic field. A dentritic field factor (Dff) was defined characterizing the dendritic plexus of a neuron both in phylogenesis and ontogenesis. The histological data have been discussed in relation to the physiological maturation of the cerebral cortex.