OBJECTIVE. The objective of our study was to investigate the effect of activity on tendon vascularity in 17 abnormal patellar tendons. CONCLUSION. Tendon vascularity is significantly increased by activity (p < 0.001). From this finding, we infer that imaging abnormal tendons with color Doppler sonography to detect neovascularization may be most useful after the patient exercises. Investigations to determine how much activity is necessary to ensure maximal vascularity is detected by Doppler sonography are required.