Forty-eight Angus bulls about 13 mo of age were used to study the effects of rate of change in live weight on muscle fiber, collagen and sensory characteristics of meat. Bulls were fed a finishing diet before treatment, and assigned to three treatments: negative, zero or positive weight gain for 30 or 60 d prior to slaughter. Treatments were imposed by adjusting feed intake. Seventy-two hours after slaughter, carcasses were observed for quality and yield grade characteristics and longissimus muscle samples were obtained for fiber type, collagen and sensory characterization. Carcass lean at the 12th rib interface became darker in color (P less than .01), softer (P less than .05), coarser textured (P less than .01) and more physiologically mature (P less than .01) when bulls were fed an additional 30 d. Increases in average daily gain improved lean texture (P less than .05), but had insignificant effects on lean color. Marbling scores and percentages of kidney and pelvic fat increased (P less than .01) with length of time fed. Quantities of carcass fat were reduced by reducing daily weight gains through restricting dietary intake. Neither length of time fed nor rate of change in live weight affected (P greater than .05) muscle fiber characteristics. Increased age of bulls tended (P greater than .05) to be associated with an increase in red muscle-fiber quantity. Length of time fed or rate of change in live weight did not affect collagen characteristics or tenderness of meat.(ABSTRACT TRUNCATED AT 250 WORDS)