Drug-discrimination studies were performed on rats, where 5,6,7,8-tetrahydro-1,3 -dioxolo[4,5- g]isoquinoline (TDIQ) served as a training drug. This compound was said to maintain partial generalization in MDMA-trained rats (75%). Number of responses on drug-appropriate lever and number of rats reaching criterion were recorded for training and test drug, with discrimination defined as >80% on the drug-appropriate lever after drug and <20% on drug-appropriate lever after saline. After establishing that rats could distinguish TDIQ from saline, training to the drug-appropriate lever was rapid, and the dose maintaining 90% drug-appropriate response was 9 mg/kg TDIQ. 5/5 TDIQ -trained rats maintained 76% drug-lever response after 1 mg/kg MDMA, and 3/5 rats maintained 74% drug-lever responding after 1.15 mg/kg MDMA. Responding was disrupted at 1.35 mg/kg and at 1.5 mg/kg MDMA. In addition, TDIQ-trained animals did not generalize stimulus response to amphetamine (27%) or methylphenidate (14%), but TDIQ did generalize to cocaine (4/5 rats with 99% drug-lever response at 2 mg/kg cocaine) despite TDIQ not stimulating locomotor activity. The TDIQ stimulus was partially attenuated by haloperidol (0.01 mg/kg reduced TDIQ responding to 46%), but the D1 antagonist R(+)SCH-23390 did not antagonize the TDIQ stimulus. The authors also tested TDIQ stimulus generalization to other compounds, including fenfluramine, trazadone, desipramine, clenbuterol, nisoxetine buspirone and diazepam. None of these substances generalized to TDIQ as strongly as did MDMA or cocaine. The findings suggest that TDIQ, MDMA and cocaine produce somewhat similar stimulus characteristics in rats through a complex process involving dopaminergic, serotonergic and noradrenergic input, perhaps also with direct action on specific receptors (i.e. 5HT1A, Beta-adrenergic receptors).