Thiazolopyrazines having growth inhibitory activity against microorganisms are of the formula ##STR1## wherein X is --Br, --Cl or F and R is --H or --CH.sub.3-x Y.sub.x, Y is --Br, --Cl, or F and x is 0, 1, 2 or 3. These compounds also have utility as intermediates for the preparation of three-ring compounds which are highly active against microorganisms.