The time between the appearance of the striated-muscle-specific M-line protein myomesin and the previous mitosis was measured in individual chick breast muscle cells. The shortest time interval (16 h) was measured with time-lapse cinematography followed by indirect immunofluorescence on 84 cells during the first two days of culture. During these experiments diffuse, cell border and cross-striated fluorescent patterns were observed in both bipolar and non-bipolar cells. A quantitative comparison of the spatial distribution of myomesin to cell morphology and time of culture revealed considerable variation among individual cells. These results indicate that the mechanisms regulating these factors during terminal differentiation are separable and not strictly coordinated.