The purpose of this study is to establish whether the application of dispersants to spilled oil is an ecologically safe means of controlling oil spills and to further investigate and document the effects of oil pollution in intertidal and subtidal habitats. To examine this, three sites were selected. The first was treated with Prudhoe Bay crude oil at one liter per square meter (L/m(sup 2)) of surface are within the site. A second site was treated with the same oil mixed with a dispersant concentrate. An approximate concentration of 50 parts per million (ppm) of dispersed oil was maintained within the site for 24 hours. A third site was used as an untreated reference site. Results as of the 12-month post-spill visit indicate that intertidal organisms, primarily red mangroves, were severely affected at the oil-treated site. Defoliation and mortality of adult and juvenile mangroves were readily evident 4 months after site treatment and after 12 months, no recovery of adult trees was observed. In the area of heaviest defoliation, many new juvenile mangroves have colonized the substrate. Adult trees were unaffected at the dispersed oil site. Resident organisms were affected at both sites, with effects being greater in magnitude and duration at the oil site. Subtidal habitats were exposed to high concentrations of dispersed oil during site treatment at the dispersed oil site, and many resident organisms were severely affected. Mortality of echinoderms, especially urchins, and sponges was widespread. These effects persisted through the 6-month follow-up visit but by month 12, large numbers of small sea urchins were present at the dispersed oil site. The abundance and growth rate of several coral species were reduced at the dispersed oil site, and abundance was reduced at the oil site. Subtidal plants, primarily turtle grass, were not affected by exposure for oil or dispersed oil. No significant changes were noted in growth rates, leaf area, or density.