Abstract This study was initiated to elucidate the complete genomic structures of type XV collagen in man and mouse and the functional properties of their promoters, as well as to obtain knowledge of the biological role of type XV collagen during development and maturity using immunofluorescence and transgenic techniques. The cloning and characterization of genomic clones revealed that the human COL15A1 gene is 145-kb in size and consists of 42 exons, and the mouse Col15a1 gene is 110-kb with 40 exons. The genomic organization of the two genes was found to be highly conserved, except for two regions of divergence. The nuclease S1 protection analysis revealed multiple transcription initiation sites in both genes, which is in accordance with the overall genomic structures of their 5'-flanking sequences. Transient cell transfection experiments with varying lengths of 5'-deletion constructs identified the fragments necessary for basic promoter activity in both genes and those implicated in the positive and negative regulation of the mouse Col15a1 gene. Furthermore, the involvement of transcription factor Sp1 in the gene regulation of the human COL15A1 gene was demonstrated. A mouse specific polyclonal antibody against type XV collagen was generated and utilized in the localization of type XV collagen protein in developing and mature mouse tissues. Type XV collagen was deposited early in the development and was particularly prominent in capillaries. Spatio-temporal differences in the expression of type XV collagen in various capillary types was demonstrated. Early expression was also detected in the skeletal muscle and peripheral nerves, while expression in the heart, lung, and kidney appeared to be developmentally regulated. Transgenic mice lines expressing truncated type XV collagen driven by either short or long endogenous type XV collagen promoters were generated. The two promoters conferred different tissue-specificities and expression levels, the longer one resulting in more endogenous-like expression. Despite some expression at both mRNA and protein levels, the truncated type XV collagen did not cause any obvious phenotypic or histological changes in any of the lines driven by the shorter promoter fragment. In heterozygote matings of one of the lines driven by the longer promoter fragment, however, a portion of the transgene positive mice appeared to be lost prenatally. Furthermore, pregnancy terminations in this line indicated a high number of abortions beginning at about 11 days of development. Further studies are needed before detailed conclusions on the consequences of the generated mutation can be drawn. The elucidation of the genomic structure of the human COL15A1 gene provides the necessary database for screening mutations in patient samples for candidate diseases caused by this collagen. The genomic clones and the mouse-specific antibody against type XV collagen are valuable tools also in future projects. The knowledge of the developmental dynamics of type XV collagen is of great value, as it helps to understand the physiological consequences that the as yet unidentified mutations in type XV collagen may cause in humans.