The occurrence of Pseudomonas aeruginosa and coagulase-positive Staphylococcus aureus in seawater from beaches of central Israel was investigated from June 1983 until June 1985. P. aeruginosa was monitored in 652 samples of seawater from 34 beaches, and S. aureus was monitored in 628 samples. P. aeruginosa was found in 44.8% of samples (6.5% with 1 bacterium per 100 ml of water), and S. aureus was recovered from 60.7% of samples (5.3% with 1 organism per 100 ml), compared with 91.6% of samples with total coliforms (TC) and 82.2% with fecal coliforms (FC). The correlation between the presence of P. aeruginosa to that of TC and FC was 99.1 and 98.3%, respectively, while S. aureus was found in 4.3 and 8% of samples where TC and FC, respectively, were absent. Monitoring of S. aureus as a supplementary indicator in populated beaches is recommended because it will add valuable information on the sanitary quality of the seawater.The bacterial quality of recreational waters is assessed by the same indicators recommended for drinking water, namely, total coliforms (TC) and fecal coliforms (FC). These organisms indicate mainly the possibility of fecal contamination, hence the presence of enteric pathogens, which are most important in drinking water. However, infections in recreational waters are not limited to enteric diseases but extend to the skin, ear, nose, and throat, and many microorganisms that cause infection in these organs do not originate in the intestinal tract of warm-blooded animals. Stevenson (28) found that ailments of the upper respiratory tract represented about 50% of illnesses recorded for bathers, while gastrointestinal disturbances were only about 20%. Mujeriego et al. (20) observed that the most frequent complaints recorded for recreational users of coastal water in Spain were skin diseases (morbidity rate of 2%), followed by ear and eye infections (1.5%), while intestinal infections were less than 1%. Foster et al. (13) maintained that the large majority of illnesses that are swimming related are transmitted by contact, not ingestion. They also maintain that the problem of disease spread by contact has been relatively ignored.The following bacterial species have been recommended as supplementary indicators for recreational workers: Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, and others. We elected to study the merit of P. aeruginosa and S. aureus as supplementary criteria for Mediterranean water by assessing their occurrence in the coastal water of our region in relation to the conventional bacterial indicators. These species were chosen for two reasons: they are both potential pathogens, and they represent pollution from two different sources, with P. aeruginosa originating in the environment and S. aureus associated with various organs of the body other than the alimentary tract.P. aeruginosa is a ubiquitous saprophite in many normal systems (6) that is widely distributed in soil, water, sewage, the mammalian gut, and plants (16) and which is able to proliferate in distille...