Basal keratinocytes reportedly comprise two ultrastructurally recognizable populations, usually referred to as serrated basal keratinocytes (SBK) and non-serrated basal keratinocytes (NSBK). The former are responsible for dermal-epidermal anchoring, whereas the latter serve in epidermal turnover (stem cells). The size and shape of these cells were investigated by electron microscopy and computer-assisted morphometric analysis. The results showed that perimeters of both the nucleus and cytoplasm of NSBK were consistently smaller than those of SBK. The shape factor (contour index) was lower in NSBK, indicating a more regular membrane surface. Present quantitative results substantiate previous subjective reports on the ultrastructural differences between NSBK and SBK and provide additional evidence that the basal cell layer in human epidermis is actually made up of at least two types of morphologically distinct keratinocytes.