The effect of six endodontic irrigants on smear layers created by hand instrumentation was evaluated in vitro in the middle and apical sections of 53 root canals. The irrigants evaluated were: 1% and 5% sodium hypochlorite, a combination of 24% phosphoric acid and 10% citric acid, 0.2%, 17%, and 3% ethylenediaminetetraacetic acid. After instrumentation and treatment with the respective irrigants, the root canal specimens were examined by scanning electron microscopy to determine the presence or absence of smear layer. The two sodium hypochlorite solutions did not remove the smear layer, even when 5% sodium hypochlorite was scrubbed on the dentinal walls. The 0.2% ethylenediaminetetraacetic acid solution was more effective than sodium hypochlorite, but it did not completely remove the smear layer, especially at the orifices of the dentinal tubules. The other three solutions effectively removed the smear layer, but no significant difference was found between them (p > 0.05). The solution of 3% ethylenediaminetetraacetic acid was as effective as phosphoric-citric acid and 17% ethylenediaminetetraacetic acid. Ethylenediaminetetraacetic acid, however, did not show the marked demineralizing effect on the dentinal walls and tubules as the acidic solution.