SummaryMethylation of membrane phospholipids is an important stage in the process of histamine release. This methylation reaction can be modulated by S‐adenosyl‐methionine (SAM) as well as by S‐adenosyl‐homocysteine (SAH). The influence of SAM and of SAH upon the histamine release of leucocytes from asthmatic and normal subjects were compared. In concentration of 10‐4M, SAM enhanced spontaneous and the specifically induced histamine release. In concentration of 10‐5M SAM enhanced the histamine release only in normals. This phenomenon could indicate a deficit in methyl‐transferase activity in the asthamatics.In concentration of 10‐4M, SAH reduced spontaneous and specifically induced histamine release, having an effect comparable to that of 10