Recently, we characterized a polymorphism within IL-1 alpha intron 6 as a variable number of a 46 bp tandem repeat (ranging from 5 to 18 repeats). We now analyse whether this polymorphism could play a role in IL-1 alpha gene regulation. We have found that reporter gene expression driven by the IL-1 alpha promoter or a heterologous promoter was decreased by increasing numbers of the repeat sequence corresponding to the most frequent alleles seen in the human population. Furthermore, we showed that the transcription factor Sp1 can bind to the 46 bp sequence. Finally, we were unable to show a statistically-significant relation between in vitro IL-1 alpha production and the number of repeats although there was a clear trend towards an inverse relation. Taken together, these results are consistent with a negative regulatory role for IL-1 alpha intron 6 repeat sequence on IL-1 alpha basal gene transcription.