Synchronous measurement of laser Doppler flux (LDF) and capillary red blood cell velocity (CBV) was performed in adjacent areas of the same nailfold during a local cold stress test in 12 healthy controls (eight women and four men) and in 22 patients (17 women and seven men) with secondary Raynaud's phenomenon before and after treatment. Two questions were addressed: Are there any differences in the signal pattern between LDF and RBV? Is it possible to detect early on in therapy, before clinical benefit becomes obvious, whether a treatment is successful or not? Despite the fact that the resulting signal patterns recorded by these two techniques are widely compatible, certain differences could be observed. In healthy controls, decrease of values during cooling time and increase after cooling were more distinct in RBV than in LDF. Compared with control values, CBV and LDF in patients with Raynaud's phenomenon were lower. After cooling CBV took an average of 3 min to reach initial value again as compared with 40 s in healthy controls. During 4 min observation time, pretest values of LDF were not achieved again in patients, whereas it took 50 s in healthy controls. If, after a few days of vasospasmolytic therapy, test results improved or normalized, clinical symptoms subsided gradually during the next weeks. Clinical improvement was not observed in those patients in whom cutaneous blood flow remained decreased despite therapy. CBV indicated this more clearly than LDF. Duration of flow stop at the end of cooling showed a marked improvement in patients treated successfully. Discrepancies between CBV and LDF are interpreted as being due to LDF detecting other vessels in addition to the superficial, nutritional capillaries. LDF seemed to be a poor tool for evaluating the effect of treatment. Determination of CBV and flow stop duration during local cold exposure may help in early selection of the best treatment for a patient with Raynaud's phenomenon by predicting later possible clinical benefit.