In vitro toxicity tests must be properly developed and scientifically validated for relevance and reliability before they are independently evaluated for possible inclusion in toxicity testing schemes and promoted for regulatory and legal acceptance. Some lessons learned in the administration of the FRAME Alternative Test Validation Scheme are reported, using as an example correlations between the results obtained in cell growth inhibition tests, both with each other and with rat oral and mouse intraperitoneal LD(50) values. Some recommendations are given for consideration for the design of future validation schemes.