A portable chlorophyll meter was calibrated with extractable chlorophyll measurements from six corn (Zea mays L.) hybrids, and the utility of the meter in identifying differences in leaf greenness was assessed in growth-cabinet and field studies. A single linear regression described the relationship between meter readings and extractable chlorophyll concentration for leaves of all hybrids at a range of growth stages (r2 = 0.83). Meter measurements resolved differences in chlorophyll concentration of two additional test hybrids resulting from different temperature regimes in the growth-cabinet, and from different leaf positions and stages of development in the field (P < 0.01). Considerable replication of meter readings was found necessary to resolve treatment differences in chlorophyll concentration. Caution is advised in using the calibration at very low chlorophyll concentrations such as those occurring as the plant nears senescence. Key words: SPAD 501, chlorophyll, leaf senescence, linear regression