Abstract: Objectives: Paraphenylene diamine (PPD) is commonly used in our region as hair dye, and to itensify Henna color. Several cases of poisoning with this compound have been reported. Therefore, we have examined the actions of PPD on a variety of pharmacological preparations in an attempt to determine the basis of its toxicity. Methods: Several isolated rat, rabbit, frog and Guinea pig preparations were used, together with anesthetized cat for blood pressure measurement. Results: After incubation of PPD with chopped G. Pig lung tissue, the supernatant was found to contract G. Pig illeum. This action was abolished by chlorpheniramine, suggesting that PPD released histamine. PPD, or the chopped lung tissue preparation, given alone, did not contract G. Ileum. Various doses of PPD did not affect striated muscle preparations, nor did it affect isolated tissues preparation, given alone, did not contract G. Ilenum. Various doses of PPD was also without effect on prostaglandin syntheis or receptors. No significant change in blood pressure was observed following PPD injection at low doses in anaesthetized cats, whereas high doses were lethal. Conclusion: PPD was ineffective in significantly altering the reactivity of several pharmacological preparations. It suggested the PPD releases histamine.