A 2-d exposure test using the marine red alga Champia parvula was developed to assess the toxic effects of pollutants entering the marine and estuarine environments. The initial exposure was followed by a 5 to 7 day recovery period to allow the development of any cystocarps (evidence of sexual reproduction) the endpoint measured. The 2-d exposure test was validated by comparison with a previously developed 2-week test in which 'no sexual reproduction' was used as the reproductive endpoint. The 2-d procedure is intended for use in testing both single compounds and complex effluents. Complex effluents, however, cannot be accurately tested with the 2-week test; therefore, only single compounds were used to compare the two procedures. Nine single compounds were tested. Concentrations that resulted in a 95% or greater decrease from the control response with the 2-d exposure were considered the best estimate of the no sexual reproduction response from the 2-week test. All of the single compounds tested, except cadmium, yielded essentially the same results with both tests.