The new rapid chloride permeability test, in which chloride ions are driven into concrete samples electrically over a 6-hour period, is becoming widely used and has been accepted as an American Association of State and Highway Transportation Officials (AASHTO) standard, T277. This paper summarizes the results of an extensive series of laboratory tests with the new method. Results of an interlaboratory test program provide single operator and multilaboratory coefficients of variation suitable for use in a precision statement in the standard versions of the method. Several possible revisions to the AASHTO standard procedure are examined, but further study is necessary before any can be accepted. Test results on specimens with diameters other than the standard 3.75 in. (95 mm) called for in T277 are found to be easily adjustable to allow comparisons with standard size specimens. Several fundamental properties of concrete, namely water-cement ratio, coarse aggregate type and gradation, and air content, are shown to affect chloride permeability.