Seven reactive dyes, analogs of C.l. Reactive Blue 171, were prepared by the well-known methods used to give monochlorotriazine dyes and used to dye cotton by the classical method (H2O + dye + fiber + 20 g NaCl/l. +15 g Na2CO3/l, pH 9-10, 85degreesC) and in buffered dyebaths (20 g NaCl/l. + pH buffer, 100degreesC). The bath ration 1:10 gave the best results. C.l. Reactive Blue 171 was used as the reference dye. Dyebath exhaustion degs. were 90-95%. At higher pH the deg. of the dye-fiber fixation was higher for monochlorotiazine dyes but dyes with the nicotinic acid residue substituted for the Cl atom, were less sensitive to changes of pH. With the latter dyes optimum pH range of the dyebath was 7.0-7.5. Dyes with the nicotinic acid required the shorter dyeing time, the alkalis were redundant, and dyeing efficiency was about 90%.