Our objective was to separate the effects of physical fill and acetate production in the regulation of voluntary feed intake. Eight ruminally fistulated Holstein cows in midlactation were fed a low forage diet or a high forage diet with or without continuous ruminal infusion of buffered acetate or propionate in a duplicated 4 x 4 Latin square with 21-d periods. Cows consumed about 3.5% of body weight as dry matter, and voluntary dry matter intake (DMI) was approximately 6% greater when cows were fed the low forage diet than when cows were fed the high forage diet. Infusion of 7.1 Mcal of net energy for lactation as acetate or propionate resulted in a reduction in DMI relative to the DMI when the high forage diet was fed alone; propionate infusion reduced intake more than did acetate infusion. Consumption of neutral detergent fiber was approximately 1.19 and 1.25% of body weight when cows were fed the low and high forage diets, respectively. Milk production was approximately 35 kg/d regardless of the diet fed, but an increase in milk fat production by cows receiving the acetate or propionate infusion resulted in an increase in fat-corrected milk. Neither neutral detergent fiber fill nor a threshold for acetate utilization appeared to limit DMI.