To investigate biological characteristics of syringomas, three-dimensional (3-D) architectures of epithelial tumor nests and luminal structures of syringomas, hair follicles, and epidermal basement membrane in skin lesions were reconstructed using a computer stereographic analysis. Each lesion was composed of many spherical-to ovoid-shaped tumor nests, which interconnected with each other by narrow tumor strands, showing features of ginger roots or budding fungi. Small discrete tumor nests were often present in the peripheral areas of the lesions. Tumor nests developed around hair follicles and beneath epidermis, but they were never connected with hair follicles or epidermal basement membrane, although occasionally such structures were slightly bent by a pressure from the developing tumor nests. There was no relationship between tumor nests and normal sweat glands. Many tumor nests formed luminal structures; however, some small tumor nests did not. Most of the luminal structures were disconnectedly present. These findings suggest that in each lesion syringoma may occur in a single focus in the upper dermis without a relationship to the surrounding normal epithelial tissues, develop and party swell forming lumina, and then the peripheral parts of the tumor may become discrete. The ratio of [lumen volume] tumor nest volume] measured by computer stereometry was 0.275 _+ 0.037 (n = 5); this indicates a constant ability to form luminal structures by syringoma cells.