The authors verified the hypothesis regarding an unawareness of possible febrile alterations during night sleep in patients with Hodgkin's disease who complain of night sweats as their only symptom. In these patients, body temperature was monitored by means of a 0.01 degrees C-sensitive linear transducer coupled with a digital multimeter. The palm of the hand (after it was passively closed in a fist by a full bandage) was the body site where temperature measurement was found to be most comfortable for a sleeping patient and independent of movements during sleep. A good correlation was found between the hand temperature taken with this technique and oral temperature. Of six patients with sweating as their only symptom, sweating recurred during the night in four and during the afternoon in the other two. In all patients sweating was preceded by a critical 0.5 to 1.5 degrees C increase in hand temperature, which took place no more than 30 minutes before sweating. Those with nocturnal sweats awakened during the subsequent sweating-related, rapid temperature decrease. These results are consistent with the occurrence of slight unperceived febrile pulses that precede sweating. The only peculiarity of night sweats consists in the higher probability that a preceding slight temperature rise may not be perceived by a sleeping patient, who is more likely to be awakened by the discomfort of the subsequent sweating. This would also explain the small prognostic significance of these sweats, which is the same as that of the preceding fever. These results are discussed in light of the increasing clinical evidence that patients with Hodgkin's disease are often affected by an instability of the thermoregulatory hypothalamic centers.