The prevalence of Aspergillus endocarditis (AE) is increasing in the hospital population. Aspergillus species contribute to approximately 25 % of all cases of fungal endocarditis. This study is a descriptive report of the use of nested PCR to detect DNA specific for Aspergillus species in serum for the diagnosis of cardiac infections. Open heart surgery was performed on patients and collected samples were examined microscopically and cultured. Ten sera in total from five patients were extracted for Aspergillus DNA and nested PCR with Aspergillus species primers was carried out. The lowest limit of detection for the PCR assay was 1 c.f.u. (ml serum) (-1). The PCR was positive in three patients. Culture of valvular tissue confirmed the growth of Aspergillus fumigatus in one patient and Aspergillus niger in two patients. In this study we have demonstrated the presence of invasive aspergillosis in patients who had undergone open heart surgery and the usefulness of a molecular assay for the diagnosis of AE.