AbstractFifty‐three heterocyclic sulphonyl derivatives including eight sulphonamides, three sulphonyl azides, nine sulphonohydrazides and twenty sulphonohydrazones of substituted thiophenes, and a smaller range of analogous isoxazoles pryazoles and thiazoles, were tested as potential fungicides in a simple screening procedure againstMucor mucedo, Septoria nodorum, Trichoderma viride, Chaetomium globosumandAspergillus niger. Several thiophene‐2‐sulphonyl based compounds exhibited a high level of antifungal activity at 100 mg litre−1against the five test species, especially the mono‐halogen‐substituted sulphonamides and sulphonohydrazines, in which a single chlorine or bromine atom was substituted in theparaposition of an attached phenyl ring. The most active compound, against all five species of fungus wasN‐(4‐chlorophenyl)‐N‐(trichloromethylthio) thiophene‐2‐sulphonamide which had average MIC50and MIC100values of 86 and 180 μmol respectively. (MIC50and MIC100values are, respectively, the concentrations required to inhibit fungal growth by 50% and to inhibit it totally.) In general, the isoxazole analogues of the thiophene‐2‐sulphonyl compounds exhibited a much lower fungitoxic activity, whilst the pyrazole and thiazole based compounds had little or no activity. Compared with the other results, the considerable activity shown by 4‐[2′‐(3,4‐dichlorobenzylidene)hydrazinosulphonyl]thioph
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