The development of transient synovitis in the hips of young children occurs quite frequently. This experiment examined the effects of a model synovitis on the deformability of articular cartilage of the immature rabbit hip. At 1, 2, 3, and 4 weeks following synovitis, there was an increase of cartilage deformability on both the acetabular and femoral sides of the joint. This increased deformability may alter force transmission to the underlying bone and its contained vascular structures.