Slightly less than 90 percent of all dairy farmers had some affiliation (via membership or nonmember patronage) with agricultural cooperatives in 1986. This was a small increase from 83 percent in 1980. When dairy farmers participated economically it was often on an “all-or-nothing” basis, both for marketings and-though somewhat less-supply purchases. In general, as size of farm increased a greater percent participated; though the proportions dropped off within the largest size category. Dairy farmers were loyal to membership, using membership for total marketings and supply purchases and, in particular, for high proportions of their dairy product marketings and feed purchases. The greatest participation overall was in the Lake States and Northern Plains; the lowest participation was in the Southeast, Mountain, and Pacific States.