BACKGROUND: Although acupuncture-needle manipulation is an important component of acupuncture therapy, little information is currently available on whether or not specific types of needle manipulation produce different effects on the body. Bidirectional (back-and-forth) rotation is one of the most common forms of needle manipulation used in acupuncture practice. OBJECTIVES: In this study, we hypothesized that bidirectional acupuncture needle rotation causes dose-dependent active cytoskeletal remodeling in connective tissue fibroblasts similar to that previously demonstrated with unidirectional rotation. INTERVENTIONS: Subcutaneous tissue explants from 18 mice were randomized to varying amounts of bidirectional rotation cycles (8-64) and rotation-cycle amplitude (180 degrees -720 degrees ) ex vivo for 30 minutes, followed by tissue fixation, confocal microscopy, and measurement of fibroblast cell body cross-sectional area. RESULTS: As with unidirectional rotation, fibroblasts responded to bidirectional rotation with extensive cell spreading and lamellipodia formation. Bidirectional needle rotation had a significant overall effect on fibroblast cell body cross sectional area (analysis of variance, p < 0.001). The cellular response to bidirectional rotation was nonmonotonic with maximal responses occurring within specific stimulus windows with regard to cycle amplitude and cycle number. CONCLUSIONS: These findings demonstrate that subtle differences in acupuncture-needle manipulation techniques can affect cellular responses in mouse subcutaneous connective tissue. Further studies will be needed to determine whether these connective-tissue responses are related to therapeutic effects.