The aqueous ammoniation of wheat straw by urea, as affected by temperature and moisture level, was studied in a 4 x 2 x 6 factorial experiment. Treatments included temperatures of 4, 14, 24 and 35 °C, moisture levels of 250 and 375 g/kg wheat straw, and treatment periods of 0, 1, 2, 4, 6 and 8 weeks. Temperature and moisture levels significantly (P ≤0,01) accelerated ammoniation, as reflected by increased in vitro OMD and total % N. Significant (P ≤0,01) temperature x treatment period and moisture level x treatment period interactions, indicated that lower temperatures and moisture levels can partly be compensated for by a longer treatment period. Slow ammonia release at 4 °C caused inefficient ammoniation at both moisture levels. Ammoniation became increasingly effective at higher moisture levels and higher temperatures, resulting in a significant (P ≤0,01) interaction between temperature and moisture level.