The present study was designed with an aim to elucidate the possible mechanism of inhibitory effect of lead on δ-aminolevulinic acid dehydratase, an earlier enzyme in tetrapyrrole biosynthesis. Supply of 0.1 – 0.6 mM lead acetate to excised etiolated maize leaf segments during greening reduced the chlorophyll content, ALA content and ALAD activity in a concentration dependent manner with the effect being most prominent for the total chlorophylls. Inclusion of Zn abolished the observed inhibition of ALAD activity by Pb, however, Mn and Mg influenced it slightly. Varying concentration of ALA during assay also affected the % inhibition of enzyme activity by lead being more prominent at higher ALA concentration. Levulinic acid, a competitive inhibitor of ALAD, and glutathione, a ubiquitous thiol compound, overcome the inhibitory effect of Pb. It is suggested that Pb inhibits ALAD activity by affecting the ALA binding to the enzymes.