A number of Israeli donors had anti-M in their sera, a proportion of which cross-reacted with N He(+) red cells. Anti-M^e was detected and while the reactivity with M and He determinants could be separated by using trypsin-treated red cells, the cross-reactivity for M and He determinants was complete in absorption experiments. One serum had anti-M separable from anti-M^e and another apparent anti-M was absorbed by trypsintreated N He(+) red cells.

A number of Israeli donors had anti-M in their sera, a proportion of which cross-reacted with N He(+) red cells. Anti-Me was detected and while the reactivity with M and He determinants could be separated by using trypsin-treated red cells, the cross-reactivity for M and He determinants was complete in absorption experiments. One serum had anti-M separable from anti-Me and another apparent anti-M was absorbed by trypsin-treated N He(+) red cells.