The M.R.C. scale for grading muscle power in stages from 0 to 5 has been compared with an analogue scale in which power is expressed as a percentage of the maximum expected for that muscle. Twenty therapists examined many patients in a series of comparative tests. The M.R.C. grade is more reliable and accurate for this type of clinical assessment in weak muscles, that is grades 0-3 on the M.R.C. scale or 0-62% on the analogue scale. The analogue scale is more reliable and accurate for the assessment of stronger muscles, that is grades 4 and 5 of the M.R.C. scale or 62-100% on the analogue scale. Therefore, analogue scales could be usefully adopted when testing bulky muscles operating at 50% or more of their normal power.