The quantitative technique of the British Standard (BS 3286:1960) has been applied to four phenolic disinfectants. Comparisons showed that regressions made with log‐probit transformations were preferable to log‐log. The British Standard quantitative technique as employed by us has been found to act as a useful adjuvant toKelsey&Sykes(1969) capacity test in the selection of use‐dilutions for disinfec