Texas Parks and Wildlife Department restricts movement of eastern oysters Crassostrea virginica among Texas bay systems because of potential disease transfer and genetic differences in natural oyster stocks. Oyster diseases, such as bonamiosis, which was found serendipitously in 2007 in Florida waters, and MSX (Haplosporidium nelsoni) have not been characterized in Texas bays. Therefore, it is prudent to periodically examine C. virginica and other bivalve species (e.g., Ostrea equestris and Isognomon sp.) from Texas bays for the presence of the causative agents of these diseases, that is, Bonamia spp. and H. nelsoni, as well as known diseases such as dermo (Perkinsus marinus). Eastern oysters (n = 30/bay) were collected from October to December 2016 from five Texas bays and analyzed for the presence of these parasites. In addition, 89 historical oyster tissue samples collected from two Texas bays in 2010 and 2011 and 37 flat tree oysters Isognomon alatus collected from a single Texas bay in December 2017 were examined. All specimens collected in 2016/2017 were assessed by PCR and histology for the presence of Bonamia spp., H. nelsoni, and P. marinus, whereas 2010/2011 samples were only assessed by PCR. Neither Bonamia spp. nor H. nelsoni were detected in any collected samples. Although 15% of the 2016 eastern oyster samples and 29% of the 2010 to 2011 eastern oyster samples contained P. marinus, the parasite was not found in any flat tree oyster. Sanger sequencing of isolated DNA was performed on samples that were positive for dermo as well as the positive controls for Bonamia sp. and H. nelsoni, which confirmed results. These results serve as a point reference that indicate Bonamia spp. and H. nelsoni are not currently present in Texas bays, but continued biennial monitoring is suggested.