cDNA microarrays was developed to investigate the relative expression of the corresponding total RNA in prostate cancer cell line PC-3 (AR-) treated with therapeutically doses of Genistein 50uM compared with untreated PC-3 prostate cancer cells. For generating fluorescently labeled cDNA samples to be used in microarray screening we used the SuperScriptTM Indirect cDNA Labeling System (InvitrogenTM). Hybridization procedure was performed overnight using a humidified Corning chamber at 450 C in water bath. The image analysis was performed using GenePix Pro 41121 and ImaGene and for Data analysis we used GeneSight. GeneSpring and MATLAB (MatArray and maanova) software for expression analysis. The gene expression analysis revealed that Genistein at therapeutically and physiologically doses as well caused a differential expression of: “6-phosphofructo-2-kinase/fructose-2. 6-biphosphate 3”. “ATPase. Ca++ transporting. ubiquitous”. “BTG family. member 2”. “H2A histone family. member L”. “H3 histone. family 3A” UDP-Gal:betaGlcNAc beta 1.4- galactosyltransferase. polypeptide 2. calcium channel. voltage-dependent. L type. alpha 1C subunit. calmodulin 3 (phosphorylase kinase. delta). caspase 5. apoptosis-related cysteine protease. chaperonin containing TCP1. subunit 7 (eta). general factor IIH. polypeptide 4. 52kDa. phosphatidylinositol transfer protein. membrane-associated. polymerase (RNA) II (DNA directed) polypeptide A. 220kDa. potassium voltage-gated channel. KQT-like subfamily. member 2. tyrosine phosphatase. non-receptor type tyrosine phosphatase. non-receptor type 7. ras homolog gene family. member N. transcription elongation factor B (SIII). polypeptide 1 (15kDa. elongin C). transcription factor B2. mitochondrial. tumor necrosis factor. alpha-induced protein 2. Cdc42 guanine nucleotide exchange factor (GEF) 9. DEAD/H (Asp-Glu-Ala-Asp/His) box polypeptide 38 acrosomal vesicle protein 1. protocadherin 1 (cadherin-like 1). putative nucleolar RNA helicase. regulator of G-protein signaling 3. ubiquitin specific protease 11. vesicle-associated membrane protein 2 (synaptobrevin 2). We conclude that Genistein can preferentially cause a decrease of some gene involved in apoptosis pathways and an increase in others in human prostate cancer PC-3 cell line. We make a bioinformatics analysis for the identified genes involved in apoptosis induced by Genistein into PC-3 cells. During this analysis we determine the gene sequences. transcripts