The aim of this study was to assess the applicability of palladium touch microelectrodes, connected to battery-run pH meters, for in vivo plaque pH measurements in children. The pH was assessed in 20 7-year-old and in 19 14-year-old caries-active and caries-inactive rural Kenyan children. The resting pH was measured at non-carious interproximal and occlusal sites and in open dentine cavities. Independent repeated measurements were performed at given sites at intervals of 15 s and 5 min and on different days. The resting plaque pH varied widely among the children, and there was no significant difference between caries-active and caries-inactive groups. The most striking feature was the considerable erratic fluctuations of pH at a given site with time, both in resting and in sucrose-challenged plaque. These fluctuations were sensitively recorded by palladium touch microelectrodes. After a sucrose rinse, not all sites in the same mouth behaved in a similar fashion, and thus the classical 'Stephan curve' was not always apparent. In conclusion, the palladium touch microelectrodes are highly applicable for plaque pH measurements in children, even under extreme field conditions.