The red carotenoid pigment, lycopene, which can be found in high amounts in tomato and tomato based products, is known to be a non-provitamin A phytochemical. However little is known about its bioactivation as well as its role in regulating the nuclear receptor pathway of gene expression. The objective of this study is to investigate the potential vitamin A activity of lycopene in vitamin A deficient mice. Transgenic RARE-luc mice which express luciferase gene under the control of RARE (retinoic acid response element) were fed with vitamin A deficient diet immediately after birth for a period of 18 weeks. During the last 10 days, 3 mice groups were treated with lycopene (40mg/kg bw), ß-carotene (40mg/kg bw) or retinol (20mg/kg bw), in concentrations which are equimolar with retinol, by oral gavage. Animals were sacrificed and ex-vivo bioluminescence imaging of the organs was performed to check if lycopene can activate the RARE as potently as retinol and ß-carotene. Based on our imaging results, lycopene can potently activate RARE in testis, brain, eye, thymus, white adipose tissue and kidney comparable to retinol and ß-carotene. Further investigations by QRT-PCR analysis to check for regulation of several retinoid regulated target genes are in process. Except for the alleviation of diarrhea after specific carotenoid or retinoid treatments, macroscopical evaluations of vitamin A deficiency symptoms were not generally conclusive. Therefore, histological evaluations of various organs as well as HPLC examinations are already in process.