Twenty-seven carcass traits were studied, for differences between lines, on 515 Hereford steers from an inbred line and three of its crosslines, from 1952 through 1966, at the Northern Montana Branch Experiment Station, Havre, Montana. Line and crossline steers were managed the same except feeding periods were 196 days for five years; 224 days for three years and to a constant weight for seven years. Starting in 1958 the line and crossline steers were compared each year to reputation rancher cattle as follows: 1958-1959, seven rancher lines and one topcross line; 1959-1964, three rancher lines and three topcross lines and 1963-1966, one rancher line, its topcross and two groups of steers purchased at auction. No differences were found between the station lines for any carcass traits in the 196- and 224-day feeding periods except shoulder width. Also no differences were found between lines for slaughter age, carcass grade, dressing percent, marbling score, shear force value and percent lean, fat and bone from the 9th, 10th and 11th rib in any analysis. When fed to a constant wright, significant differences (P<.01) between lines were found for carcass weight, length and width measurements, fat thickness and l. dorsi measurements. Significant differences (P<.01) between lines for carcass length and width measurements showed no line or crossline to be superior in these traits and most differences were so small they could not be determined by visual appraisal. ..