A new solid-phase reagent strip for determination of glucose in whole blood, Visidex, has been developed specifically for visual use in conjunction with a calibrated color scale. Two reagent pads are used, each formulated for a different portion of the range of clinical values, to maximize the visual resolution available to the user. Colorimetric examination of reacted reagent pads indicated that the label color blocks match closely the appearance of the reagent pads; that the reagent pads exhibit good precision; and that the colors of the reagent pads are independent of operator technique, sample volume (20-50 microL), and effects of potential interferents studied (although high concentrations of fluoride slightly inhibited color development). Glucose measurements obtained visually with the Visidex system correlated well with values obtained with a YSI Glucose Analyzer (for two separate studies, slope = 0.96 and 1.04, r = 0.99 and 0.96, and n = 172 and 543, respectively).