Both players have tested positive for methylhexaneamine, a "non-specified stimulant" on the prohibited substances list of the World Anti-Doping Agency (Wada).
Methylhexaneamine is scheduled to be reclassified as a "specified stimulant" from 1 January 2011, which means it will join the list of drugs that are more susceptible to being taken by mistake.
Bjorn Basson and Chiliboy Ralepelle both tested positive for the banned stimulant methylhexaneamine and as a result, UK Sport tested six South Africa players following their defeat by Scotland instead of the usual two.