AbstractFibrillar networks are intimately involved in several morphogenetic processes which underlie the harmonious development of the vertebrate embryo. Recent genetic evidence has demonstrated that the minor types V and XI collagen are key regulators of types I and II fibrillogenesis in non‐cartilaginous and cartilaginous matrices, respectively. A comprehensive understanding of the expression and regulation of the genes coding for the chains of the minor collagen types is therefore relevant to animal morphogenesis and development. The present study was undertaken to elucidate the embryonic pattern of expression of the gene coding for the mouse α1 chain of type XI colagen (Col11α1) using the technique of in situ hybridization. Transcripts of the Col11α1 gene were detected as early as 11 days of gestation. The α1(XI) transcripts were found to accumulate mostly in cartilaginous tissues, such as the chondrocranium and the developing limbs. Like the major cartilage‐specific collagen (type II), Col11α1 expression was also noted in the neuro‐epithelium of the brain. However, α1(XI) transcripts accumulated in several other non‐cartilaginous sites. They include odontoblasts, trabecular bones, atrioventricular valve of the heart, the tongue, the intestine, and the otic vesicle. Altogether, the data confirm that Col11α1 has a broader spectrum of expression than previously thought. This finding raises the possibility that the α1(XI) chain may participate in the formation of stage‐ and tissue‐specific trimers with distinct functional properties. © 1995 wiley‐Liss, Inc.