A composition comprising a microbicidally synergistic mixture of A) methylisothiazolinone (MIT) or benzisothiazolinone (BIT) with B) methyl glycine diacetic acid (MDGA). wherein the synergistic ratio of MITI MDGA range is from 1/15 to 1/250 and wherein the synergistic ratio of BIT/ MDGA range is from 1/20 to 1/1600.