The reactions of a set of organoalkaline compounds with trans-p-carotene (Car) were studied in solution (using UV/Vis, ESR, and mass spectroscopy) and compared with the reactions of the same set with insoluble polyacetylene. It was shown that the naphthalene radical ion and the dicarbanionic dimer of 1, I-diphenylethylene, 1,1,4,4-tetraphenyl-l,4-butanediide, react with Car by a simple electron transfer leading to Car radical ion and dianion. This dianion is protonated by methanol mainly at carbon 7 or 7'. On the contrary of diphenylalkyllithium compounds add to Car double bonds. This addition of I mol of diphenylalkyllithium per Car takes place mainly at the central double bond. sec-Butyllithium (sec-BuLi) reacts also by addition to Car. The addition products are in some cases instable and decompose to radical ions through a non-elucidated mechanism. These transfer or addition reactions with Car, as well as the exclusive electron transfer observed with polyacetylene, are rationalized on the basis of the relative redox potentials of reactants. a) Part I : cf.".