Type II collagen is one of the principal markers of chondrocyte differentiation (Mayne, 1990) and is encoded by the proα1 (II) collagen gene (Col2a1)(Cheah et al., 1985). In the mouse, Col2a1 transcripts are first detected at 9.5 days post-coitum (dpc) in the sclerotome of the differentiating somites and the cranial mesenchyme destined to give rise to the cartilage. Expression is also observed in the notochord and later in some neural tissues, including regions of the rhombencephalic basal plate and the ventricular layer of the hindbrain (Cheah et al., 1991). The regulatory elements that direct chondrocyte-specific expression in tissue culture cells and transgenic mice are located within the first intron of the