Germlings of Uromyces appendiculatus respond to topographical stimuli and develop appressoria. During this period several genes are expressed, one of which is Inf24. Germlings were microinjected with a sense and antisense fragment of the ORF of Inf24. Sense (Inf24-S), 5′-ATG AGT GCT TCA TCG CAG CAG CAG-3′ fragment did not affect germling response to the topographical stimuli and the developed appressoria. Microinjection of antisense (Inf24-RC), 5′-CTG CTG CTG CGA TGA AGC ACT CAT-3′ blocked gene transcription and appressoria were rarely formed. Injection of Inf24-RC into already formed appressoria did not inhibit continued development of subsequent infection structures, e.g. penetration peg, sub-stomatal vesicle.