Exposure of rabbits to hashish smoke every other day for a period of one month resulted in a marked increase in blood ammonia. This increase is not probably due to any hepatic damage since there was no concomitant increase in the number of serum enzymes known to be elevated during hepatic damage. It might be related to the inhibitory effect of hashish on incorporation of amino acids into proteins resulting in an increased availability of amino acids to the catabolic pathways coupled with an increase in the glutamate dehydrogenase activity. These factors could also account for the increased blood urea concentrations in these animals.