Ortel et al (1998) have shown that induction of keratinocyte differentiation augments intracellular PpIX accumulation. Similarly, DMSO was found to induce differentiation of B16 melanoma cells and enhance PpIX accumulation (Schoenfeld et al, 1994) and Mamet et al (1994) demonstrated increased activity of PBGD in malignant cell lines. Interestingly, higher heme biosynthetic enzyme activities such as PBGD and lower PpIX precursor concentrations were found in Barrett's oesophagus and adenocarcinoma of the oesophagus (Betz et al, 1999). Here, HMBS is linked to Barrett esophagus.