["To investigate influence of whole-body cooling on cyclic GMP (cGMP) in women with Raynaud's phenomenon and in healthy women.", "The study was performed as an open, parallel-group comparison between women with Raynaud's phenomenon and healthy women during the winter month of February.", 'The municipality of Västerås (Sweden).', 'The Raynaud group comprised 24 female patients. The control group consisted of 21 healthy females.', 'The venous levels of cGMP were measured on three different occasions: just before and after 40 min of whole-body cooling and after 20 min rest at room temperature (21 degrees C).', 'Venous cGMP increased significantly in the control group after cold exposure (mean difference 0.43 pmol mL-1; 95% CI, 0.018-0.848; t = 2.18; df = 20; P = 0.02) and remained at a high level after 20 min rest (mean difference 0.58 pmol mL-1; 95% CI, 0.063-1.108; t = 2.34; df = 20; P = 0.015). In contrast, the levels of venous cGMP in the Raynaud group did not change significantly. The difference in increase between the two groups was significant (P < 0.02). The diastolic blood pressure in the Raynaud group increased after 40 min of whole-body cooling and was still significantly increased (P < 0.001) after 20 min rest at room temperature (21 degrees C).'] Does cold exposure increase cyclic guanosine monophosphate in healthy women but not in women with Raynaud 's phenomenon?