Cationic starch (CS) is routinely used in the papermaking process to improve the dry strength or printability of paper. The effectiveness depends on the distribution of the starch on the pulp fiber, and in this study, time-of-flight secondary ion mass spectrometry was used to investigate this distribution. The characteristic peak at 58m/z was applied to map the CS. Based on the imaging analysis of the handsheets with the CS as an internal additive, the distribution of CS became more uniform with decreasing freeness. The amount of adsorbed CS increased with increasing fiber length and was lower on vessels than on other fibers. These results were related to fibrillation. From the analysis of handsheets with CS as an external additive, the penetration depth of the starch into base paper increased with decreases in the sizing degree of the base paper. (C) 2008 Elsevier B. V. All rights reserved.