Presents a first attempt to catalog the Spanish algae herbaria created before 1936. The most important collections are at the Real Jardin Botánico, Madrid; Institut Botanic, Barcelona; and Facultad de Farmacia, Universidad Complutense. J. Rodriguez Femenia's herbarium, deposited in the Ateneo de Mahón (Minorca), also is noteworthy. The relationship between the different projects for elaborating Iberian or Spanish flora catalogs and the increase of herbarium holdings and their review is obvious. The reviews and reorganizations of these herbaria throughout their history have often led to a loss of information.