Toxicity determined in vitro by morphological alterations and neutral red absorption.

A method is described which combines the use of a visual morphological cytotoxicity assay with a quantitative neutral red (NR) spectrophotometric test, for the assessment of the effect of toxic agents on 3T3 cells in culture. These sensitive and reproducible assays lend themselves to a screening procedure of potential toxicants which can help reduce the use of animals for toxicity testing.