Most frame languages either are glaringly deficient in their treatment of default information or do not represent it at all. This paper presents a formal description of a frame language that provides semantically sound facilities for representing default information and an efficient serial algorithm for inheriting default information down class-subclass and class-member hierarchies constructed in that language. We present the inheritance algorithm in two forms. In the first form, the algorithm provides justifications to a TMS, which then manages the inherited information. In the second form, the algorithm performs its own, special-purpose truth maintenance and therefore is useable in a system that does not, include a general-purpose TMS.