Late in the spring of 1934 a patient was seen in San Francisco who presented a clinical picture like that of dengue. A syphilitic patient inoculated with his blood showed the symptoms and signs of inoculation with dengue which have been studied experimentally in many parts of the world. Subinoculations in three other successive patients reproduced the same type of illness in each. As there are no recent reports of dengue occurring in the United States and as the disease has never been recorded as occurring endemically in Northern California, the possibility of its appearing here is of great importance. Although this is the only instance to date in which an attempt has been made to substantiate the diagnosis by inoculation into human subjects, five additional cases of apparently the same condition have been recognized. These endemic cases together with the four experimentally produced ones form the basis of this