In 1983 the Conservation Laboratory of the National Széchényi Library was assigned the task of restoring 32 paper and parchment codices of the Budapest University Library, among them 12 Corvinus manuscripts. The latter had been rebound by the Turks before they were returned in 1877. Each codex was examined by microbiologists and chemists. They reported that the worst damage was caused by Streptomyces fimicarius and Penicillium Alternaia. The former microorganisms were noted to avoid ink containing lamp black. Damage to parchment was generally greater than that to paper. The text details how heavily infected codices were treated by a gas mixture of 15% ethylene oxide and 85% carbon dioxide in a partial vacuum, and how deformed and brittle parchment pages were restored. Incomplete pages were completed by a new method called parchment casting. 18 codices have been restored so far. -- AATA