Antibiotics are routinely used for the decontamination of allograft heart valves. To monitor the efficacy of this process, samples of tissue are sent for microbiological analysis. This investigation was undertaken to determine residual antibiotic concentrations in decontaminated tissue and to assess the likely inhibitory effect on microbiological cultures. After a typical decontamination protocol, both gentamicin and vancomycin were present in all tissue samples and the majority of enrichment broths at concentrations sufficient to inhibit most bacteria. The data presented indicate that protocols used by heart valve banks and associated microbiology laboratories should be reviewed, and support the use of predecontamination cultures to identify particularly virulent micro-organisms.