Background: To study the toxicity and pharmacokinetics of LU103793 (Cematodin®), a novel cytotoxic anticancer drug being an analogue of Dolastin 15 which was isolated originally from the Indian Ocean sea hare Dolabella auricularia. Method: 9 patients with refractory metastatic solid tumors were treated in a phase I study. The drug was administered as rapid (5 min) intravenous bolus injection at 3-weekly intervals. 14 courses of LU103793 were totally administered. The starting dose was 2.5 mg/m2 and escalated to 20 mg/m2 within 4 steps. Results: The dose-limiting toxicity was a) reversible hypertension, and b) cardiac infarction. No significant myelotoxicity was observed. Other toxicities were nausea and vomiting, drug fever, pain at the tumor site and asthenia. Concentrations of LU103793 and its main metabolite were measured in all 9 patients in whole blood samples. Two exponential terms are necessary to describe the c(t) profile. The pharmacokinetic parameters at 20 mg/m2 are: maximum concentration 9.0 ± 7.2 μM, the area under the curve 37.3 ± 6.8 μM × h, the plasma clearance 0.8+0.14 1/hour/m2, the volume of distribution at steady state 9.6 ± 2.0 1/m2 and the elimination half-life 10.3 ± 1.5 h. The AUC was increasing from 4.6 μM × h at 2.5 mg/m2 dose level to 37.3 μM x h at 20 mg/m2 dose level, suggesting a linear kinetic in the range of the tested doses. No objective tumor regression was observed. Conclusions: The dose-limiting toxicity (DLT) was reached at 20 mg/m2 with cardiovascular side-effects. Hypertension and a myocardial infarction determined the DLT. The mechanism of the observed cardiovascular side effect is still unclear. In case that high peak blood levels are critical with respect to the observed toxicity, prolongation of the drug administration either as continuous infusion or a split mode (repetitive drug application over 3-5 days) should avoid this problem. Phase I trials with such application modes are i