1. 1. Two groups of 250 stool samples each, proceeding from equal numbers of individuals, were collected at random in a known endemic focus of schistosomiasis mansoni and examined for eggs of Schistosoma and other helminths by the following procedures: direct saline smear (three 22 mm 2 preparations), HCl-triton-ether centrifugation, sodium sulfate-triton-ether centrifugation, HCl-sodium sulfate-triton-ether centrifugation, formalin-triton-ether centrifugation and sedimentation by gravity in glycerinated water. 2. 2. Both groups of samples were examined by the smear method and by HCl-triton-ether and sodium sulfate-triton-ether centrifugation. Sedimentation in glycerinated water was applied only to the first group of 250 stools; HCl-sodium sulfate-triton-ether and formalin-triton-ether centrifugation, only to the last group of 250 stools. 3. 3. Percentages of available cases diagnosed were determined on the basis of the total number of cases uncovered among each group of samples by the combination of methods applied. Average values of the number of eggs recovered by the concentration procedures were also calculated on the basis of the available cases. 4. 4. The percentage of available cases of schistosomiasis mansoni diagnosed, with the corresponding average number of eggs recovered, was as follows: three direct smears, 47%; HCl-triton-ether, 80%, 53; sodium-sulfate-triton-ether, 91%, 70; sedimentation in glycerinated water, 85%, 44; HCl-sodium sulfate-triton-ether, 76%, 45; formalin-triton-ether, 91%, 62. 5. 5. As respects the other helminth infections, the results may best be appreciated from the accompanying tables directly. 6. 6. The following conclusions may be derived from the data and observations: (a) Sodium sulfate-triton-ether and formalin-triton-ether proved the most effective concentration procedures for the detection of S. mansoni infections. Since they are so simply, cheaply and speedily performed, they appear to be the coprological methods of choice for survey or field work pertaining to this parasitosis. (b) Hydrochloric acid-triton-ether proved highly effective for the recovery of Trichuris and hookworm eggs, but decidedly unfavorable for the recovery of Ascaris eggs, infertile ones in particular, (c) Sodium sulfate-triton-ether proved highly effective for the recovery of Trichuris as well as S. mansoni eggs, but decidedly unfavorable as respects those of hookworm and Ascaris, infertile ones in particular. (d) Neither sedimentation in glycerinated water, as hereby executed, nor HCl-sodium sulfate-triton-ether proved outstanding in any respect, the latter behaving very much like HCl-triton-ether. (e) The direct saline smear proved superior to all the other methods for the detection of strongyloidiasis and, with the possible exception of glycerin water sedimentation, for the detection of fertile and infertile Ascaris infections. Its importance in other para-sitoses as a simple, rapid and efficient screening method before the application of concentration or noncoprological diagnostic procedures, or in distinguishing heavily from lightly infected individuals, is reaffirmed. (f) Of the concentration technics studied, formalin-triton-ether stands out as the nearest to an all-around diagnostic procedure, having proved highly effective in the detection of all the helminthiases here mentioned, with the exception of strongyloidiasis, and, on the basis of investigations made by others and incidental observations made by the present authors, of protozoan cysts as well.