R. Ian Domowitz, Glenn Hubbard, and Bruce C. Peterson (1988) estimate industry markups of price over marginal cost and show the influence of market structure on cyclical movements in total factor productivity, using a disaggregate panel data set of 284 four-digit, Standard Industrial Classification industries. In this comment, the authors examine whether Domowitz, Hubbard, and Peterson really estimate what they intend to estimate. Domowitz, Hubbard, and Peterson also claim their 'estimates are not as large as those of Hall.' If it is not clear what they estimate, the comparison is of limited usefulness. Nevertheless, the Domowitz, Hubbard, and Peterson study deserves consideration and contemplation by anyone interested in industrial economics.