Automated total collection (ATC) of digesta from four steers fitted with duodenal re-entrant cannulas was compared with flow estimations based on Cr₂O₃and acid detergent lignin concentrations of ATC samples. In two successive periods, each steer was fed about 4 kg daily of an all-roughage or an 80% sorghum grain diet. Digesta samples were automatically taken and pooled every 2 hr, during 3- to 6-day collections. Sample aliquots, representing 4% of the digesta measured in each 2 hr were pooled to represent 24-hr digesta flow. Data of 2-hr samples were used to study diurnal flow patterns. Duodenal digesta and dry matter flow rates estimated by Cr₂O₃and lignin were greater by (TURN) 15% than flow rates measured by ATC. Mean recoveries of Cr₂O₃and lignin at the duodenum were 93 and 89%, respectively. Animals fed the roughage diet had about 55% greater digesta flow rates than when fed the concentrate diet (42 versus 65 l daily average by ATC). There appeared to be an interaction between diets and markers. Apparent ruminal dry matter digestibility calculated from direct measurements by ATC was 44% for the concentrate diet and 37% for the roughage diet. Rumen digestbility values based on Cr₂O₃and lignin were about 25% lower than the ATC values. Average coefficients of diurnal variation for digesta flow were 29% in the concentrate diet and 34% in the roughage diet. Estimations from Cr₂O₃and lignin based on 2-hr samples could either under- or overestimate digesta flow by 31 to 350% of the 24-hr flow based on ATC. Thus, special emphasis should be given to the problem of sampling procedures when using indicators and spot-sampling technique to estimate digesta flow. There was evidence of a 24-hr cycle for the whole digesta flow in the grain diet, with a period of low flow before the onset of the light hours. No consistent flow pattern could be identified in the roughage diet. Lignin concentration patterns in digesta were somewhat similar for both diets; however, Cr₂O₃patterns were different between diets. Digesta dry matter concentration followed a similar pattern to that of Cr₂O₃in the grain diet and to that of lignin in the roughage diet, suggesting that the flow patterns of solid phase components of digesta may also be differentially affected by the dietary concentrate: roughage ratio.