Expression of testicular Interleukin-l a was anaIysed both at the lavel of biological activernpeptide and its encoding mRNA, using a sensitive bioassay, Thymocyte proliferation assay, andrnPolymerase Chain Reaction. In order to analyse the relative change in the level of IL -1 a mRNArnexpression a Quantitative PCR technique was developed involving an intemal standard IL -1 a RNArnconstruct derived from rat macrophage IL -1 a cDNA preparation.rnThe IL -1 a mRNA expression during postnatal rat development could be detected by PCR asrnearly as 20 days, postnatal, and The intensity of amplified cDNA band was found to increase withrnincreasing days of postnatal age.rnBy using Quantitative PCR, a relative increase in the level of amplified IL-lacDNA could berndemonstrated starting from day 20, and this increase in the level of amplified cDNA is found to reachrna sustained high level from 30 to 60 postnatal days of rat testicular development. This study showsrnthat the level of IL -1 a mRNA rises in parallel to the level of IL -1 a peptide during maturity, previouslyrndemonstrated, and suggests that it is controlled at the level of mRNA expression, probably attranscriptionalleve/.rnThe role of testosterone in the regulation of tiL -1 a was analysed using rats treated with, EDSrnwith and without testosterone replacement, and androgen receptor blocker, cyproterone acetate. Thernresult showed that EDS pretreatment resulted in an increase in the level of both IL -1 a bioactivity andrnthe level of its mRNA. Exogenous testosterone replacement along with EDS treatment significantlyrnreduced the effect of EDS treatment on the expression of tiL-I a peptide and mRNA. Cyproteronernacetate treatment in contrast resulted in a decrease in the IL -1 a mRNA levels.rnThis study shows that tiL -1 a expression is developmentally regulated at the level of its mRNArnexpression. It also suggests that testosterone regulates testicular IL -1 a expression at the level ofrntranscription. This finding further strengthens the importance of testicular IL -1 a as a paracrine growthrnfactor in the regulation of testicular development and function.