A two site electrochemical enzyme immunoassay for thyrotropin (TSH) has been developed. This assay is based on the use of an immobilized capture antibody and a biotinylated second antibody. Detection is achieved via avidin labelled with alkaline phosphatase. The substrate 1-naphthyl phosphate was used and the product 1-naphthol was detected at disposable screen-printed carbon 8-electrode combs using specially designed instrumentation.