A survey was made to assess the biotype status of populations of the whitefly Bemisia tabaci (Gennadius) in Spain. The study involved observation of the squash silverleaf reaction, analysis of esterase patterns and application of a RAPD-PCR technique. The results obtained by the three methods were fully consistent and showed that the Spanish populations of B. tabaci were composed of two genetic types. One corresponded to populations of the B biotype, found in Tenerife (Canary Islands), Barcelona, Madrid, Malaga and Almeria. The other, showing a unique RAPD and esterase pattern, was found in Majorca (Balearic Islands), Seville, Valencia, Murcia and Almeria, as well as in the Algarve Region of Portugal. RAPD patterns of other populations from the rest of the world used for comparison showed that populations from Arizona (USA), Israel, France, Denmark, Italy, Netherlands and Japan have similar RAPD patterns typical of the B biotype. By contrast, populations from the Iberian Peninsula, Turkey, India, Pakistan and Arizona (A biotype), showed different and unique patterns.