The effect of variable fibre radius on the initial creep rate, <(epsilon)overdot>*, of monofilament ceramic fibres was investigated using a numerical integration method. The following parameters were studied: (i) radius variation geometry, (ii) creep stress exponent, n, (iii) fractional radius variation, r(v), and (iv) fraction, m, of the characteristic radius variation wavelength, the ranges of n (0 < n < 3) and r(v) (0 < r(v) < 0.5) were chosen to be similar to those for current ceramic fibres based on the silicon carbide (SiC) system. Values of <(epsilon)overdot>* were found to be consistently greater compared to those for a constant radius fibre with an equivalent mean radius and increased with both n and r(v). The main result of this work was a recommendation for creep testing of monofilament ceramic fibres to be limited to certain radius variation geometries and gauge lengths. (c) 2005 Springer Science + Business Media, Inc.