forming a capillary in which liquid may flow by capillary action this technique is sometimes referred to as a u201c capillary flow u201d diagnostic device in a single channel device there would be one or more detection zones and viii other types of channel in use a fresh sample applied at 1 is moved via capillary action into the primary reagent conduit the filter paper may be hydrophilic over at least part of its area to restrict and or concentrate the flow of sample along the primary conduit 2 the primary reagent conduit is optionally in fluid contact with a secondary reagent conduit 3 containing secondary assay reagents the secondary reagent conduit is selectively sized to facilitate capillary flow of sample from the primary reagent conduit fig1 represents a single secondary reagent conduit in an alternative embodiment of the invention more than one secondary reagent conduit may be present containing reagents required to complete the assay again capillary flow will draw the sample primary assay reagent mix into the secondary assay conduit 3 to facilitate the reaction of secondary reagents with the sample primary assay reagent mix a detection zone 4 is selectively positioned to interact with the reaction mixture once all components have been mixed and the assay completed the detection zone 4 may contain substrates necessary to allow detection of the product of the assay alternatively these substrates may.