Exposure of certain postharvest fruit-infecting fungi (Alternaria alternata, Botrytis cinerea, Colletotrichum gloeosporioides, Monilinia fructicola, Penicillium digitatum, P. expansum, P. italicum, Rhizopus stolonifer and Thielaviopsis paradoxa) to ethylene (C2H4) at 1, 10, 100 and 103 .mu.l/l of air stimulated germination of P. digitatum, P. italicum and T. paradoxa and germ tube elongation of most of the tested fungi, but had little influence on their final growth rates at 20.degree. C. Treatment with C2H4 up to 103 .mu.l/l of air increased the total dry weight of B. cinerea grown in vitro and in vivo (the latter on strawberries, as determined by glucosamine content) after 4 days at 20.degree. C. Glucosamine content of P. italicum grown in vitro and in vivo (the latter on oranges) also increased in response to similar exposure of fruits to C2H4. C2H4 did not affect lesion diameters on navel organes inoculated with P. italicum before C2H4 exposure was initiated. Similar organes treated with C2H4 for 3 days at 20.degree. C before inoculation with P. italicum became more resistant and developed smaller lesions.