Health savings accounts and health reimbursement arrangements may be starting to have a small but noticeable effect on corporate health plan costs.

Costs for account-based group plans that include prescription drug coverage appear to be up 10.7% this spring, while costs for conventional preferred provider organization plans that include prescription drug coverage appear to be up 11.2%, according to researchers at the consulting arm of Aon Corp., Chicago.

The researchers base those figures on a survey of about 70 large benefits vendors.

The gap between account-based plan costs and conventional PPO plan costs is the widest Aon has detected in its spring cost surveys since it began including account-based plans in the surveys in 2004.

In the spring of 2006, Aon was reporting an average cost increase of 12.4% for conventional PPO plans and an average increase of 12.5% for account-based plans.