1. Myogenic satellite cells were isolated and cloned from the Pectoralis major muscles of 6-week-old Nicholas and Merriam's tom turkeys to compare in vitro properties of muscle development between turkeys with markedly different growth rates. 2. Although only small differences (P < or = 0.05) were noted between proliferation rates of the two cell populations in McCoy's 5A medium-15% chicken serum, satellite cells derived from the Nicholas variety were more responsive (P < or = 0.05) to mitogenic stimuli from serum at all levels tested. 3. When satellite cells were stimulated by low serum levels to differentiate into multinucleated myotubes, cells from the Merriam's turkey fused more rapidly (P < or = 0.05).