We observed novel phenomena on the growth of a hemA deletion mutant (H500) of Escherichia coli: First, H500 cells grown in rich medium required an increased amount of exogenous 5-aminolevulinic acid (ALA) for normal growth, as compared with cells grown in poor medium. Second, H500 cells grown with an insufficient supply of ALA had a prolonged lag phase but relatively normal growth during the logarithmic phase. An increased requirement of exogenous ALA in rich media was due to an impermeability of the cells to ALA, resulting in a reduced ability to synthesize porphyrins. The latter could be also explained by change in permeability that was repressed under heme-deficient conditions.