More employers are offering workers financial incentives—worth hundreds of dollars in some cases—to take steps to improve their health and stem the rising cost of their care. Seth Serxner, a senior consultant at benefits firm Mercer, says companies began such efforts a few years ago with modest incentives simply for completing health risk questionnaires. Now some have boosted rewards but require workers to do more to get them. Hospital giant HCA, for example, in April began offering diabetic workers in the corporate offices $400 a year toward medical costs if they go to 10 counseling sessions with diabetes educators.