The dorsocutaneous (DLD) and anterior (ALD) latissimus dorsii are both homogeneous slow tonic muscles. Autografts of mature DLD were attached onto the ALD of chickens to study regeneration of slow tonic muscle fibres innervated exclusively by slow tonic nerves. Fifty-three grafts were examined from 3 to 231 days after implantation for myosin ATPase, and for heavy chains of fast myosin. New muscle fibres in grafts were initially type 1 (slow) or type 2 (fast twitch). Tonic type 3 fibres were slow to differentiate and were not seen within 59 days. From 105 days many fibres were type 3A and type 1 were no longer apparent. However, type 2 fibres persisted and appeared to be present instead of type 3B fibres even after 8 months.