1,3,3-Trimethylspiroindoline-2,3'-3 H-naphth[2,1-b][1,4]oxazine (1a) and 6'-piperidino-1,3,3-trimethylspiroindoline-2,3'-3 H-naphth[2,1-b][1,4]oxazine (1b) were applied as disperse dyes to polyester, nylon and acrylic fabrics. Under optimised dyeing conditions, photochromic fabrics were produced which, on irradiation with ultraviolet or exposure to sunlight, turned blue (1a) or blueish-purple (1b). Dye 1a showed enhanced photochromic colour change performance compared with dye 1b. The photochromic colour build was highest on nylon and lowest on acrylic fabric. The colour change properties and the technical performance (wash fastness and photostability) of the photochromic fabrics were evaluated using specifically adapted colour measurement methods. The data were analysed in terms of variation of lightness, a*, b*, chroma, hue angle and ?E, colour difference before and after exposure, and K/S curves as a function of irradiation time. The fabrics generally showed good wash fastness. Although the colour build-up decreased with exposure to the Xenotest fadeometer, some residual photochromism remained after prolonged exposure. © Journal compilation © 2008 Society of Dyers and Colourists.