Fumigation ofVicia fabaseeds with14C‐methyl bromide for two weeks followed by four‐week aeriation period resulted in the formation of bound residues equivalent to 33% of the terminal residue or approx. 30 ppm. Of this amount, 3.4% was incorporated into the seed DNA. The effect of cooking on the treated‐aerated beans showed that 50% of the initial dose remained bound to seed tissues. A bioavailability study of14C‐bound residues showed that over 70% of the ingested dose was bioavailable to the rat. The major radioactivity was eliminated in urine (36.6%), feces (24.1%) and CO2(19.3%). Analysis of the urine showed that 36% of the radioactivity was in the purine fraction; one fifth of this amount was associated with 7‐14C‐methylguanine. Subacute feeding of bound residues to mice for 8 weeks at a dietary level of 30 ppm resulted in a significant decrease in the number of white blood cells and an increase in the activity of SGOT and SGPT of the treated mice. Blood urea nitrogen was also increased while blood creatinine remained unaltered.