The characteristics of companies that either accepted or declined participation in a 5-year randomized trial of a multirisk factor health promotion intervention were compared to investigate potential limitations on the generalizability of research findings. A representative sample of 151 manufacturing work sites in the northeast was recruited to participate. Sixty-four of the companies were determined to be eligible and 10 others, which refused to have an administrator interviewed, were presumed to be eligible. Of this group, 27 companies agreed to participate. Workforce demographics, shift structure, and prior history of health promotion offerings were not significantly different in the two groups. However, participating companies employed fewer workers and had a more favorable financial outlook than did companies that declined to participate. Implications of these findings for research on work site health promotion are discussed.