A unique case of midgut carcinoid with advanced disease, engaging lymphnodes and liver but still accessible to curative surgery, is reported. Besides elevated urinary levels of 5-hydroxyindoleacetic acid, the diagnosis was based on a positive provocation test with pentagastrin, i.e., basally elevated levels of serotonin in peripheral whole blood increased twofold 3 min postinjection related to the appearance of carcinoid symptoms. After removal of primary and secondary lesions in a two-step procedure carcinoid symptoms disappeared completely. Biochemically, urinary excretion of 5-hydroxyindoleacetic acid and serotonin levels in peripheral blood before and during provocation with pentagastrin were both normalized after surgery and have remained so during 27 months of follow-up. Computed tomographies of the abdomen at regular intervals do not indicate recurrent disease. Histologically, the carcinoid lesions displayed a mixed growth pattern and signs of local aggressiveness. Immunocytochemically, the majority of the tumour cells (positive against neuron specific enolase) showed a positive reaction with serotonin antisera. Substance P-like immunoreactivity was also found in a large proportion of these cells.