Values for mean fibre diameter (FD) and FD variance were determined on wool samples obtained from five different locations on the bodies of progeny in fine wool, strong wool and fine X strong wool Merino sheep. The respective genetic groups numbered 48, 23 and 37 and were maintained as one flock on irrigated lucerne, rye grass and small grain pastures. Mean FD and FD variance values were lower (P ≤0.05) in fine wool progeny than in fine X strong wool contemporaries, which in turn had lower (P ≤0.05) means for both traits than strong wool progeny. Values for mean FD and FD variance of fine X strong wool progeny were roughly on midparent values. Both traits increased from the anterior to the posterior position of the fleece, with the means for samples obtained from the shoulder being lower (P ≤0.05) than those of britch samples. The mean FD values of belly and midrib samples were generally lower (P ≤0.05) than those of back samples, except in the fine wool progeny. The variance of FD decreased (P ≤0.05) dorsoventrally in strong and fine X strong progeny. In fine wool progeny, a similar tendency was small and insignificant. Concern for excessive FD variation in progeny of fine wool rams mated to strong wool ewes is unwarranted. The processing performance of wool so produced is unlikely to be negatively affected.