Method and apparatus for quantitating the amounts of enzyme substrates and metabolites present in biological fluids using spot test techniques. The tests utilize both fixed, preselected color standards and substrate and metabolite standards freeze-dried on transparent membranes or in porous pads for comparison. Other reagents including enzymes, dyes, cofactors are also freeze-dried in absorbent pads. The assembly may utilize any or all of the following in various combinations: porous discs of materials such as glass fibre filters to store reagents, to serve as liquid reaction volume measurement, and to assist in removing cells from blood samples; microporous membranes to act as barriers to blood cells; a protein enrichment membrane or a dialysis membrane to restrict passage of large molecules to the indicator zone; and a transparent window which may be a second microporous membrane or impermeable plastic on which indicator dyes are dried. In assembled format, the test plates, slides or discs fulfill all requirements for conducting the selected test: no added instrumentation, controls or other measurements are required.These test devices may assist in the diagnosis of a number of pathological conditions which give rise to abnormal levels of metabolites or enzyme substrates. Methods for rapid assay of serum cholestrol, uric acid, testosterone, androsterone and galactose have been indicated as examples. A wide variety of other compounds found in biological fluids may also be assayed by similar technology.