SummaryThe hyaluronidase - hæmoglobin test allows an easy investigation of the spreading properties of the skin connective tissue. Comparative measurements at successive intervals on different patients can be easily obtained on condition to use purified and standardized preparations.The treatment of rheumatoid arthritis with A. C. T. H. permits to observe in parallel to the clinical remission, a significant decrease of the area of spreading, which coincides with the fall of circulating eosinophils. Spread increases again after post-therapeutic recurrence.In one case however, the remission obtained by A.C. T. H. rapidly changed into a clinical relapse, notwithstanding the continuation of the treatment. In parallel, the areas of spread, which had been reduced, give high readings. This unfavourable evolution seems te be due to a momentary adrenocortical exhaustion.Cases of acute rheumatic fever, put to bed with or without salicylate, may show a spontaneous progressive reduction of spread to low readings, comparable to those observed after A. C. T. H. Those modifications seem te be the result of an endogen adrenocortical activation, favoured by the utmost reduction of the hormonal expenses necessary for the adaption to the exterior medium.The reduction of spread of the mixture hyaluronidase - hæmoglobin in case of adrenocortical therapy does not seem to result from a simple inhibition of hyaluronidase, but from the synthesis within the ground substance of the connective tissu, of mucopolysaccharides presenting a high agregation level, which makes them relatively resistant to hyaluronidase activity.