The transitional behaviors of myoblasts toward differentiation were investigated in the cultures at the low and high seeding densities (respectively, X-0 = 1.0 x 10(3) and 2.0 x 10(5) cells/cm(2)). In the culture at the low seeding density, an increase in confluence degree accompanied a decrease in growth potential (R-p), being R-p = 0.85 and 0.11 at t = 48 and 672 h, respectively. Myoblasts seeded at the high density resulted in the immediate cessation of growth with keeping the low range of R-p = 0.02-0.09 throughout the culture. The reduction of Rp led to the generation of three subpopulations of cells in proliferative, quiescent and differentiated states. Close cell contacts in the confluent state of high seeding culture induced cell quiescence to a higher extent with suppressing differentiation. (C) 2009. The Society for Biotechnology, Japan. All rights reserved.