Bovine somatotropin (BST) has been commercialized in several countries and is widely used under a variety of management conditions in Mexico and Brazil. In the United States, most of the published data on BST results is from clinical trials conducted with university herds under guidelines established by the Food and Drug Administration to demonstrate safety and effectiveness of BST at various dosage levels. The shortage of specific research addressing management practices that augment BST response necessitates that much of the discussion on this subject be speculative and based on our knowledge of the care and handling of untreated cows. Although some Dairy Herd Improvement Association groups are beginning to assess the level of BST response that can be predicted from production data, others have not begun to monitor the process. BST field trials conducted in Pennsylvania illustrate another point. Response to BST appeared to be more dependent on the hours of feed availability than on herd-production average.