This study evaluated the adhesion of newly mixed glass ionomer restorative materials to set materials. The flexure strength of specimens formed by the addition of new material to week-old material by using two different surface treatments was compared with the flexure strength of solid specimens that were 1 week old. All repaired specimens attained at least 44% of the average strength of unrepaired specimens of the same material. Repairs made with a combination of unlike materials were not significantly different from most repairs with like materials. For all materials collectively, repairs made with a 37% phosphoric acid pretreatment were significantly stronger than repairs made with a 40% polyacrylic acid pretreatment.