Complete midsubstance injuries of medial collateral ligaments of matched New Zealand white rabbits were allowed to heal without repair or immobilization for various lengths of time. Morphological and biochemical parameters were used to evaluate healing as compared with normal unoperated and sham operated ligaments. Results showed incomplete healing at the longest term follow-up (14 weeks) with significant biochemical abnormalities. Although there was a trend toward normal, recovery from injury was much slower than previously reported.