Ankara, 12 Novembre 2007 – Alternatives 2007 11 Skin irritation  Test Definition Harmonised exposure: 15 min exposure + 42 hr post-incubation Endpoints:- Cell viability - MTT - Release of IL1  in media (when cell viability > 50%) Prediction model: MTT cell viability  50%  skin irritant (R38) MTT cell viability > 50%  non irritant Additional: MTT > 50% + IL1  > 60 pg/ml  skin irritant (R38)  Reproducibility EPISKIN (MTT)EpiDerm (MTT) Within-laboratory (a)93.9 %96.0 % Between-laboratory (b)89.5 %88.5 % Proportion of identical MTT classifications (a) over 3 independent experiments, (b) based on median classifications