Iron polymaltose complex (IPC) is a recently marketed preparation with questionable bioavailability. We compared the absorption kinetics of IPC with ferrous sulfate. We also studied the effect of oral iron on diurnal variation. The study was conducted in eight healthy, non-smoking, non-alcoholic volunteers after obtaining their written informed consent and after Institutional Ethical Committee approval. The study was conducted in three phases: during the first phase no drugs were given, whereas in the second and third phases, ferrous sulfate (66 mg elemental iron) and IPC (100 mg elemental iron) were given in a randomized, two-way, cross-over design, with a wash-out period of 1 week. The blood samples were collected, iron levels estimated and the pharmacokinetic parameters calculated. Circadian rhythm in iron levels was demonstrated by cosinor analysis with a mesor of 93.6 microg/dl, acrophase 10.40 h and amplitude of 26.4 microg/dl. Evening levels were higher as compared with morning levels. Drug treatment increased the mesor (115.7 microg/dl; p < 0.05), delayed the acrophase (11.30 h; p < 0.05) and increased the amplitude (38.5 microg/dl; p < 0.05). The bioavailability of ferrous sulfate was significantly greater as compared with IPC with greater Cmax and AUC (p < 0.05). A clear cut circadian rhythm in iron concentrations was demonstrated. Ferrous sulfate was shown to have significantly higher bioavailability as compared with IPC. Further studies having hemoglobin levels as an endpoint may be planned.