Professor Mannaioni or Piero as we all knew him, graduated in Medicine in 1959 at Florence University, and during his training developed an interest in pharmacology, cardiology and clinical toxicology. In 1959, he received a post-graduate degree in Cardiology and Rheumatology. He then joined the Institute of Pharmacology and Toxicology, now Department of Preclinical and Clinical Pharmacology, as Assistant Professor in 1961, as Professor of Toxicology in the Medical School in 1967 and Full Professor of Toxicology in 1974. He was awarded the first Chair in Toxicology in Italy. During his post-doctoral training, he received a number of fellowships for pharmacological research and was a visiting scientist at Yale University Medical School, where he became interested in mast cell histamine. Returning to Florence, he continued his research on mast cell histamine and on cardiac anaphylaxis. Professor Mannaioni has been a pioneer in the field of cardiac histamine, suggesting over 30 years ago, its involvement in myocardial diseases, such as arrhythmias, angina and myocardial infarction. He was also interested in mast cell histamine release induced by cholinergic stimulation or by free radicals and the interactions between histamine, nitric oxide and carbon monoxide. He joined this society in 1972 and played a very active role here; National and General Secretary for twelve years, and hosted the EHRS meeting in Florence (1975 and 1982). Besides his research in the field of histamine, he was always committed to the development of medical toxicology as a primary science and he was the head of the Clinical Toxicological Unit in Florence, until 2002. This unit is universally recognized as a reference clinical structure for the treatment of acute and chronic intoxication. He authored about 200 international papers, of several books and many scientific and publications in Italian. Professor Mannaioni passed away on the 27th June 2021.