The site of apparent absorption of Na, K, Ca, P, Mg, and S in lactating dairy cows fed whole-crop barley, oats, triticale, or alfalfa silages was studied. Eight ruminally and duodenally cannulated Holstein cows with ad libitum access to a total mixed diet were assigned to one of four treatments as a replicated 4 x 4 Latin square design. All diets contained the same concentrate (50%, DM basis) plus one experimental silage. The concentrations of Na, K, Ca, P, Mg, and S in the concentrate were .84, .71, .85, .78, .27, and 38%, respectively. Dry matter intake was higher (P < .05) for cows fed alfalfa and barely silages than for cows fed oats and triticale silages (19.6, 18.6, 16.7, and 17.2 kg/d, respectively). Alfalfa silage contained a higher concentration of all minerals studied than the cereal silages, except Na. Sodium flow at the duodenum was substantially greater than dietary intake and apparent total tract digestibilities ranged between 74.5 and 85.2%. Secretion of P in the forestomach ranged from 34 to 61 g/d and the major site of absorption was in the intestine. The correlation between P intake and fecal excretion of P was significant (P < .001, r/ = .39) and linear. Potassium absorption occurred before the duodenum and in the intestine. Apparent digestibilities of K were lower for cereal silages (range 74.0 to 82.9%) than for alfalfa silage (88,7%). Apparent total tract digestibilities of Ca (28 to 32%), P(27 to 34%), and MG (17 to 24%) were similar for all diets so that Ca, P, and Mg absorption (g/d) reflected dietary Ca, P, and Mg levels. Data indicate that forage source can influence the site and extent of absorption, fecal output, and apparent digestibilities of macrominerals.