PURPOSE. To investigate alterations in prelens tear film (PLTF), contact lens (CL), and postlens tear film (PoLTF) thicknesses and contact lens movement associated with boric acid-containing rewetting drops. METHODS. This was a single-center, randomized, double-masked clinical trial. Following etafilcon A lens application, baseline lens movement and interferometric measures (PLTF, CL, PoLTF thicknesses) were captured. A randomly assigned drop (either a low or high boric acid-containing drops) was applied to both eyes, followed immediately by lens movement and interferometric measures. After a 2-h washout period (spectacle wear), subjects returned for testing with the alternative drop. Statistical analyses addressed pre- to postdrop changes in lens movement and PLTF, CL, and PoLTF thickness. RESULTS. The presence of a drop alone lead to substantial decreases in contact lens movement (general reduction of 0.45 mm), but the reduction was not related to drop type. The presence of a drop led to an increase in PLTF thickness (∼0.14 μm), again regardless of the drop type. Both the general presence of a rewetting drop and drop type lead to an increase in CL center thickness (lower boric acid drop = 0.31 μm and higher boric acid drop = 1.13 μm). Both the general presence of a rewetting drop and the drop type lead to a significant decrease in PoLTF thickness, whereby the lower boric acid drop lead to a decrease of 0.28 μm and the higher boric acid drop lead to a decrease of 0.73 μm. CONCLUSIONS. Boric acid-containing rewetting drops were shown to be associated with a significant reduction in lens movement with a concurrent increase in lens center thickness and reduction in PoLTF thickness. The higher boric acid-containing drop was associated with more substantial increases in lens center thickness and decreases in PoLTF thickness. © 2008 American Academy of Optometry.