BACKGROUND Sentinel node navigation surgery (SNNS) has recently been introduced for various types of carcinoma. Numerous radioisotopes are used as tracers for SNNS. However, few reports have examined particle sizes of isotope colloids used in SNNS. METHODS Tin and phytate colloids were used in the present study. Isotonic sodium chloride and tin solutions were mixed ratios of 1:4, 1:2, 1:1, 2:1, and 4:1. Calcium solution and Tc-phytate were mixed at ratios of 1:4, 1:2, 1:1, 2:1 and 4:1. Particle size was measured using a Coulter Model N4SD Sub-micron Particle Analyzer. RESULTS When isotonic sodium chloride and tin solutions were mixed at ratios of 1:4, 1:2, 1:1, 2:1, and 4:1, particle size was 47 +/- 9, 96 +/- 10, 712 +/- 83, 925 +/- 66 and 1079 +/- 132 nm, respectively. As the ratio of tin solution decreased, colloid particle size increased. Particle size of phytate colloid varied from 174 +/- 39 nm to 1222 +/- 283 nm, according to calcium concentration. Phytate colloid particle size became larger as the ratio of phytate solution decreased. CONCLUSIONS We ascertained that the particle size of tin and phytate colloids is controllable by manipulating the conditions under which the colloids form. These results will offer useful information when SNNS is performed.