Abstract When substituting the mouse bioassay for lipophilic marine algal toxins in shellfish with analytical methods, science based factors of relative toxicity for all analogues that contribute to health risk to consumers are necessary. The aim of this paper is to establish the relative intraperitoneal toxicity of dinophysistoxin-2 (DTX-2) compared with okadaic acid (OA). The study was performed as an open, randomised parallel group trial with a four level response surface design within each of the two parallels. In accordance with the response surface design model, the LD 50 for DTX-2 and OA was 338 and 206 μg/kg, respectively. By use of common regression analysis, the LD 50 of DTX-2 and OA were estimated to 352μg/kg and 204μg/kg, respectively. The deviations between the LD 50 estimates by the two methods was 4% for DTX-2 and less than 1% for OA. Taken together, these results indicate that the relative toxicity of DTX-2 is about 0.6, compared to OA. Results from the PP2A assay correspond very well with the results obtained by the mouse bioassay. The IC 50 concentrations for DTX-2 and OA were 5.94 and 2.81 ng/mL, respectively. This indicates that OA is about twice as toxic as DTX-2. Since inhibition of PP2A is acknowledged as the main mechanism of toxicity of the OA group toxins, this supports the establishment of a relative toxicity factor of DTX-2 of 0.6 compared with OA.