1,3,4-thiadiazines and 1,3,4-selenadiazines will be converted to pyrazoles under special conditions by chalcogene elimination. The tendency of pyrazole formation depends very strongly on the substituents in 5- and 6-position of the 1,3,4-thia- or 1,3,4-selenadiazine. Trifluoroacetic acid has proved to be a suitable reagent for S and Se extrusions. 5-phenyl-6H-1,3,4-thiadiazines will also undergo ring transformations in the presence of trifluoroacetic acid, but the sulfur at this site persists at the molecule as a mercapto group. Under the conditions used by us 1-trifluoroacetyl-4- trifluoroacetylthio-pyrazoles will be formed. 5,6-disubstituted 1,3,4-thiadiazines and 1,3,4-selenadiazines will be transformed to S and Se free 1-trifluoroacetyl- pyrazoles by heating with trifluoroacetic anhydride. The structures of the 1-trifluoroacetyl-4-trifluoroacetylthio- pyrazoles obtained will be proved by secondary reactions.