The rate of exhaustion of Dye I is very dependent on the thickness of the fibre, but that of Dye II appears to be almost independent on the thickness of the fibre except the early stage of dyeing, suggesting that the increased surface area does not affect markedly the rate of dyeing of the bulky dye that diffuses slowly. It can also be noted that the rate of dyeing of Dye I on 0.5-d fibre is faster than that of Dye II on the same fibre. The results clearly show that the relatively big dye is difficult to penetrate into the fibre.