The performance testing of solar collectors containing a boiling liquid poses some new problems for the testing laboratories. These problems are described in relation to the newly proposed "ASHRAE Standard 109(P)". The similarities and differences between "ASHRAE Standard 109P" and ASHRAE Standard 93-77 are defined and discussed. Basically, it may be concluded that most of the technical problems in testing boiling liquid collectors are relatively minor. However, some of the test fluids and test loop components may be relatively unfamiliar to the solar test laboratories. Further, the "ASHRAE Standard 109P" requirement of determining thermal efficiency at multiple values of subcooling and at two separate levels of solar insolation tends to increase the time and cost of testing over that of similar tests for non-boiling collectors.