['The objective of this study was to evaluate in vitro apical microleakage of root canal filling materials for primary teeth.', 'Fifty extracted primary anterior teeth were distributed into 6 groups: 4 experimental groups; 1 negative control group; and 1 positive control group. Zinc oxide and eugenol (ZOE), Kri paste, calcium hydroxide (Ca(OH)(2)), and Vitapex were inserted into the canal using a lentulo spiral mounted in a slow-speed handpiece. All teeth were then subjected to a dye leakage test using 2% methylene blue as the tracer.', 'The highest dye penetration was recorded for teeth filled with ZOE, with mean values of 9.01+/-1.23 mm. Vitapex showed the lowest dye penetration, with mean values of 4.02+/-1.79 mm. Comparison between groups showed significant difference when the Vitapex and Kri paste groups were compared to the ZOE group (P<.0001). Also, a significant difference between the Vitapex and Ca(OH)2 group (P=.014) was detected. The result showed no difference between Vitapex and Kri paste (P=.658) nor between Kri paste and Ca(OH)(2) (P=.185).'] Do apical microleakage of primary teeth root canal filling materials?