Measurements of the diameter distribution of both sale lots and commercial tops using the Sirolan-Laserscan have shown that earlier studies using the FDA (Fibre Diameter Analyser) overestimated the coefficient of variation (CV) of fibre diameter by about one percentage point (due to instrumental errors). For 95％ of the measured sale lots of Australian merino wools, the CVs were in the region 19％ to 26％. For commercial tops, the range of observed CV for a given mean diameter was only ± 1.5 units, much smaller than that for the sale lots. For the commercial tops, CV was found to increase with increasing mean fibre diameter by approximately half a percentage point per micrometre passing through the point 21 μm and 21％ CV. In relation to potential skin comfort, although the relevant critical diameter defining the coarse fibre component is dependent on fabric type, these critical values are highly correlated for commercial tops and hence it is reasonable to continue to use the percentage of fibres greater thn indicator of the relative skin comfort of different wools. For commercial tops, due to the small spread in observed CV as a function of mean diameter, relative potential skin comfort can be adequately predicted simply from the mean fibre diameter.