This paper concerns the effects of the position and the nature of substituents on the colour of azo dyes derived from 2‐arainothiophens. Of primary interest is the colour shift from the red of phenylazo dyes to the greenish blue of the analogous 5‐substituted 3‐nitro‐2‐thienylazo dyes. The greenish blue of 2‐amino‐3‐nitro‐5‐aeyl(or aroyl)thiophen dyes is in striking contrast with the violet—red of 2‐amino‐5‐acylthiophen dyes and the violet of dyes from 2‐amino‐3:5‐bismethylsulphonylthiophen.Even simple aniline coupling components afford blues to blue‐greens with the 5‐substituted 2‐amino‐3‐nitrothiophens. However, progressively increased bathoehromic shifts to bluish green are obtained with the following coupler types— tetrahydroquinoline, benzomorpholine, and 2‐alkoxy‐5‐acetamidoaniline.Dyes from 2‐amino‐3‐nitro‐5‐acylthiophens, particularly, have excellent affinity for secondary cellulose acetate and give good exhaustion and level dyeing. They colour cellulose acetate deep, bright blues to greens. Dyed fabrics have superior gas‐fu