The aim of the work described in this thesis was to develop and evaluate two rapid, colloidal gold-based, immunochromatographic assays, a ‘cassette’ and ‘wick’ type, both for the qualitative detection of the glycoprotein hormone, human chorionic gonadotrophin (hCG) in human urine and serum. hCG is present in large quantities in the urine and serum of pregnant women and thus, provides a means for diagnosing pregnancy. A key element of this work was to develop assays, which would be capable of competing strongly in this market. The outcome of this project was a highly sensitive and specific cassette and wick hCG assay, having the capability to detect as low as 25 IU/L hCG on the first day of a missed period. These assays also had the capacity to detect levels up to 250,000 IU/L hCG before a ‘hook’ effect was observed. This analytical range was equal to the majority of the tests already on the market. Evaluation of the two assays yielded 100% sensitivity and specificity for the cassette assay with urine samples and 98.5% sensitivity and 100% specificity for serum samples. A sensitivity of 99.4% (urine) and 100% (serum) and a specificity of 100% (urine) and 98% (serum) were obtained for the wick assay. It should be emphasised that these assays are limited to the qualitative detection of hCG and subsequently, all positive results should be confirmed by a doctor. It is a measure of the success of the assays that predicted sales for the first six months of 2000 are estimated at -$60,000 for the cassette assay and -$100,000 for the wick assay.