Six patients with episodic cluster headache were investigated as to blood pressure, heart rate, cerebrospinal fluid pressure (Pcsf) and frontal vein pressure (Pvf) during five nitroglycerin (NG) provoked attacks and one spontaneous attack. In a seventh studied patient the NG failed to provoke an attack. The earlier reported decrease of systolic blood pressure and increase of diastolic blood pressure and heart rate after NG administration were also found in these patients. The "dynamite headache" was related to the start and duration of an increase of the cerebrospinal fluid pressure. There was no relationship between the start or the maximum pain of the cluster headache attack and changes in Pcsf or Pvf. On breathing oxygen during a cluster headache attack, there was a decrease of Pcsf but in some patients a temporary increase of Pvf was observed, which possibly indicates that oxygen simultaneously attains constriction of arteries and veins.