A syndrome seen in four Jamaican patients is described in which increased use of marihuana followed the onset of symptoms of a hypomanic nature. At the time of admission to the hospital the patients exhibited persecutory delusions, auditory hallucinations, withdrawal, and thought disorder. Within three to four days after admission, manic or hypomanic symptoms emerged. It is suggested that these patients had mania and that excess marihuana usage was symptomatic of their illness, leading to a transient, marihuana-induced, schizophreniform phase of their manic illness. A plea is made for a broader approach to the psychiatric implications of marihuana use.