The present invention relates to a proximity probe based detection assay (“proximity assay”) for an analyte in a sample, specifically a proximity probe extension assay (PEA), an in particular to an improvement in the method to reduce non-specific “background” signals, wherein the improvement comprises the use in such assays of a component comprising 3′ exonuclease activity, said method comprising: (a) contacting said sample with at least one set of at least first and second proximity probes, which probes each comprise an analyte-binding domain and a nucleic acid domain and can simultaneously bind to the analyte; (b) allowing the nucleic acid domains of the proximity probes to interact with each other upon binding of said proximity probes to said analyte, wherein said interaction comprises the formation of a duplex; (c) contacting said sample with a component comprising 3′ exonuclease activity; (d) extending the 3′ end of at least one nucleic acid domain of said duplex to generate an extension product, wherein the step may occur contemporaneously with or after step (c); and (e) amplifying and detecting the extension product.