In this study, we compared the performance of the Virochip and deep sequencing for detecting virus sequence in human serum. The limit of detection of the Virochip was approximately one part in 10 5 for the poliovirus controls, for which there are microarray probes with perfect sequence complementarity ( Figure S1 ). The sensitivity of deep sequencing is limited by the number of reads generated per sample, or read depth. In this study, we detected virus sequences down to two parts per million. Nearly every virus that was detected on the microarray was also detected by deep sequencing; additionally, in numerous samples (n = 44), sequencing revealed viruses not detected by the Virochip (Table 1) . There were two instances where Virochip analysis identified a virus (TTV) that was not detected by deep sequencing (Table 1) . Deep sequencing, therefore, is a superior method for novel virus discovery, because it is more sensitive and provides more conclusive genotypic information than the Virochip. The NCBI TaxID and name of the virus species with the highest number of hits among those viruses with BLAST hits is given.