Abstract: A liquid transfer device of disposable one-time use form to conduct a biochemical diagnostic or other assay comprises two liquid flow channels (10,110,210; 20,120,220) leading from a respective pair of channel ends to a common site (30,130,230) and operable to deliver liquid to this site in sequentially timed manner following simultaneous application of such liquid to the channel ends. Typically respectively different reagents (11,111,211; 21,121,221) are incorporated in the two channels, and a third reagent (31,131,231) at the common site, whereby a sample to be assayed in respect of a particular content can be applied to the site, immobilized by the third reagent, subsequently subjected to one channel reagent to detect any of the content of interest, and finally subjected to the other channel reagent to exhibit for the user any detected content.