A peptide homologous to the Drosophila melanogaster sex-peptide (SP) was isolated from Drosophila suzukii accessory glands and its amino acid sequence determined. The D. suzukii peptide contains 41 amino acids and has a calculated molecular weight of 5100 Da. Comparison of the sequences reveals strong homologies in the N-terminal and C-terminal parts of the peptides. In the D. suzukii sex-peptide, however, five additional amino acids are inserted after amino acid 7. Based on the sequence of the peptide, a cDNA coding for the D. suzukii peptide was isolated by PCR. Sequence analysis of the cDNA confirmed the SP amino acid sequence determined by peptide sequencing. Furthermore, based on the cDNA sequence, we isolated the D. suzukii sex-peptide gene by inverse PCR. The D. suzukii sex-peptide gene contains an intron and codes for a 60 amino acid precursor. The D. melanogaster and the D. suzuki sex-peptides elicit rejection behaviour in the presence of males and an increased egg laying in virgin females of both species.