The time course of serum transaminases (alanine aminotransferase and aspartate aminotransferase) has been followed in 30 selected consecutive patients presenting burn sizes ranging from 10% to 95% of the total body surface (mean 43.13) and a survival index from 0.99 to 0.00 (mean 0.59). The results show that in all the patients both transaminases change in parallel, increasing in 18 patients (60%). In nearly all patients both enzymes increase during the second week after injury and aspartate aminotransferase increases later than alanine aminotransferase. The higher transaminase levels are noted in moderately ill patients. No clear correlation between the overall increase of transaminases and the extent of burned surface area has been found. We conclude that functional liver alterations mostly contribute to the increase of serum transaminases in burns.