49 juxtaglomerular apparatuses were examined using 1.9mu thick Giemsa-stained serial sections from human renal tissue embedded in plexiglass. In 43 juxtaglomerular apparatus the direct contact areas between the different juxtaglomerular structures and the basal area of the macula densa were calculated. A positive, significant correlation was found between the size of the macula densa and the direct contact area between macula densa and Goormaghtigh's cell field on the one hand, and between the macula densa and the direct contact area between Goormaghtigh's cell field and the afferent arteriole on the other. There was also a significant, positive correlation between the direct contact area of Goormaghtigh's cell field with the macula densa and that of Goormaghtigh's cell field with the afferent arteriole. On the efferent side none of these correlations were significant. Thus a "flow of information" from the macula densa via the Goormaghtigh cells to the afferent arteriole is morphologically possible. The direct contact areas between macula densa and the afferent or the efferent arterioles were not correlated with any of the other parameters. Epithelioid cells were present in the interlobular arteries, prior to and within the juxtaglomerular apparatus in the afferent arterioles, as well as within and beyond the juxtaglomerular apparatus in the efferent arterioles.