The density of spines on apical dendrites of pyramidal neurons of which the soma was located in layer III of area 17 of human visual cortex was measured. This was done in Golgi-impregnated sections from a series of brains from foetal age 33 weeks to 30 years postnatally by counting the number of spines on a segment of apical dendrite situated between 50 and 100 micron from the soma. In the late foetus, a mean of less than 30 spines was found in the 50 micron long segment. In the brain of a neonate about 50 spines were counted on the corresponding segment. At about 5 months postnatally the maximum number of spines is reached (approximately 80 in the segments measured), after which spine number decreases, reaching a level of about 50 again by 2 years of age, a figure that is maintained into adulthood.