Several chemical disinfecting solutions for soft contact lenses were evaluated according to the tests suggested by FDA in the May 1983 revision of the Microbiological Guidelines. It was experimentally determined that cleaning and rinsing lenses remove 3.5 to 3.9 logs of microorganisms. Furthermore, it was determined that only 3% hydrogen peroxide had a rapid enough disinfection rate to meet the safety factor requirement within four hours as suggested in the "D-value test.' when contaminated lenses were cleaned, rinsed, and disinfected with commercially available solutions, all failed to disinfect the lenses within the minimum time specified on the label. These results were used to recommend significant changes in the Microbiological Guidelines. These changes include (1) limiting the rechallenge requirement during preservative effectiveness testing to only disinfecting solutions, (2) using the death rate kinetic profile of any approved chemical disinfecting solution as a basis for comparison of a new chemical disinfecting solution, and (3) using the results of the multi-item test for any approved chemical disinfecting solution as a basis for comparison of a new, proposed chemical disinfecting solution.