An absorption inhibition method for the detection of gamma marker Gm(11) in dried bloodstains is described. Particular reference is made to the association of Gm(11) with Gm(-1, -2). When a dried bloodstain fails to inhibit anti-Gm(1) and anti-Gm(2), this may represent a true Gm(-1, -2) result or there may be insufficient material to inhibit either antibody. The detection of Gm(11) in a bloodstain extract provides an objective means of confirming the apparent absence of Gm(1) and Gm(2) as representing a true Gm(-1, -2) result. This antigen compares very well with other blood group systems with regard to the amount of bloodstain required for analysis and its stability. No evidence is available for preferential loss of Gm(1) and Gm(2) relative to Gm(11) in dried bloodstains.