Since many of the copolymers studied here are hydrophilic, it was hypothesised that degradation could occur in the presence of a water-soluble nucleophilic amino such as Lcysteine. Degradation of hydrophobic DOT-copolymers in the presence of cysteine has previously been shown to be effective, but rather slow. Here, the copolymers were left for 1 week in a 10 mM aqueous cysteine solution at physiological temperature (37°C), which correspond to relevant conditions found in vivo.