Section 4231(b)(2) of ERISA and Sec. 4231.3(a)(1) require that no participant's or beneficiary's accrued benefit may be lower immediately after the effective date of the merger or transfer than the benefit immediately before the merger or transfer. A plan that assumes an obligation to pay benefits for a group of participants satisfies this requirement only if the plan contains a provision preserving all accrued benefits. The determination of what is an accrued benefit must be made in accordance with section 411 of the Code and the regulations thereunder.