Classical swine fever (CSF), also known as hog cholera, is a highly contagious viral infection of swine caused by a member of the genus pestivirus of the family, Flaviviridae. The need for accurate laboratory diagnosis of CSF is particularly important as it is more reliable than clinical diagnosis. CSF is endemic in many tropical countries where the climate is characterized by high ambient temperature and humidity. This study details the effect of sample quality on CSF antigen-capture ELISA (AC-ELISA) and reverse transcriptase-polymerase chain reaction (RT-PCR) methods. RT-PCR assessment of AC-ELISA-positive spleen samples stored in a conventional glycerol/saline buffer demonstrated that the RT-PCR was detrimentally affected by poor sample quality. To provide a more accurate representation of this effect, a 14 days study was performed to determine the effect of tropical ambient conditions on CSF virus-positive spleen samples stored in two transport media; glycerol/saline and a proprietary RNA preservation solution (RNAlater). A protective effect was demonstrated in both assays with RNAlater as samples were positive in both assays until day 14 post-exposure. Samples stored in glycerol/saline were negative at RT-PCR at day 3 post-exposure although AC-ELISA was still positive at day 14 post-exposure.