This paper estimates the productivity of men and women in the peasant agriculture of the Peruvian Sierra, using recent household survey data. A sexual division of labor on the farm implies that male and female labor are not perfectly substitutable. Evidence is found for female specialization on livestock production. A translog production function reveals that the use of animal traction and land affect the marginal productivity of male and female labor differently, suggesting that the two types of labor cannot be aggregated. Overall, adult male labor is found to contribute more to farm output at the margin than adult female labor, though the extent of the difference is sensitive to how farm output and the labor inputs are measured.