Selected chemicals in sediments and the abundances and biomasses of macrobenthic species were determined at seven stations from two littoral ecosystems in the Gulf of Cádiz. The marine macrobenthic communities were described in both ecosystems that are subjected to different sources and levels of contamination. A qualitative relationship between source of contamination and biological effects for each station is proposed and the results of the univariate and multivariate analysis used are discussed. Univariate analyses using conventional community descriptive parameters (number of species, abundance and richness, Shanon-Weaver and evenness indices) and the numerial contribution of major taxonomic groups (i.e., Polychaeta, Oligochaeta, Mollusca and Crustacea) could not be used as a means of classifying the sites as clean or polluted with respect to the contamination measured. The results showed that multivariate methods are much more sensitive than univariate techniques. Abundance/biomass comparison (ABC) plots classified the macrobenthic communities into different classes mainly related to organic contamination. However, this analysis did not reflect the alteration due to inorganic sources of contamination. This kind of analysis is valuable for the evaluation of alteration of effects but it cannot discriminate between two different phenomena: pollution (adverse effect associated with chemical concentrations) and alteration (adverse effect associated with chemical concentrations or with natural variations).