A scattergram diagram was made of controls and failures of treatment of squamous cell carcinoma in the tonsillar fossa on log-log paper coordinates of doses and treatment times. An exclusion line with an exponent of 0.30 was hand-drawn with all failures below the line. The same methodology has been used for the squamous cell carcinomas of the glosso-palatine sulcus and the base of the tongue. Isoeffect curves were obtained for lesions of all sites of the oropharynx with an exponent of 0.30 for the tonsillar fossa, 0.35 for the glossopalatine sulcus, and 0.38 for the base of the tongue. GHOSSEIN, using the least square method, obtained a curve with a slope of 0.33 for the squamous cell carcinomas of the supraglottic larynx. One can conclude that dose equivalents calculated from the equation D = D.T0.33 can be used as a first approximation in the squamous cell carcinomas of the upper respiratory and digestive tract treated between 4 to 8 weeks. It does not mean that a dose given in 4 weeks is clinically equivalent to a dose given in 7 weeks, derived from the isoeffect curve.