The tissue cell culture tests are designed to determine the cytopathic effects of a material or its extracts in contact with monclayers of diploid human cells. Since both test materials are liquids, each was applied to sterile filter pads for evaluation. The catalysts were tested for direct contact cytotoxicity by placing treated filter pads on confluent monolayers of human embryonic or fetal cells. After incubation for 24 hours, the cytopathic effects were evaluated microscopically against both a positive and a negative control. In addition, each test material (on filter pads) was extracted in dimethyl sulfoxide (DMSO) for one hour at 121C and in tissue culture medium (MEM) at 37C for 24 hours. The MER extracts were tested by aspirating the medium from acceptable wells and replacing it vich 1.0 - 1.5 al of the MEM extract from the test material. This was repeated using blank (no material) and positive control extracts. Test and control DMSD extracts were evaluated by replacing the medium on confluent monolayers vich extracts diluted to 21 in MEM. All cest wells were incubated and evaluated using the procedures described above for the direct rentact method. Both catalysts were cytopathic in direct contact, and their MEN extracts also caused morphological changes. While DMSO extracts of Catalyst 1 produced cytopathic effects in culture, those of Catalyst N appeared to be innocuous at the concentration tested. Extraction of Catalyst M at autoclave temperatures produced a large amount of yellow precipitate; as judged by the color change of phenol red in the medium, NEM extracts of this material vere quite acidic.