This invention relates to an isolated nucleotide fragment of a novel estrogen receptor, in particular, a novel ER.beta. variant protein and isolated nucleic acid fragment comprising the coding regions of the genes encoding such variant proteins. Also provided are vectors, host cells, and methods for producing the novel ER.beta. variant protein. The invention further relates to method of obtaining such nucleotide fragment and the method of determining the presence of such ER.beta. variant protein in a sample.