Essentially all higher plants and animals demonstrate a rhythm of about 24 hours, even when maintained in constant conditions. In most organisms the generation of the rhythm involves a feedback loop in which genes in the nucleus are transcribed to messenger RNA. The mRNAs leave the nucleus and are translated into proteins. The proteins move back into the nucleus to turn off the transcription of the mRNA. Delay in this system causes this feedback loop to oscillate, i.e. the concentrations of the mRNA and protein oscillate with a period of about 24 hours. In these systems (fungi, fruit flies, mice, etc.) the nucleus is an integral part of the circadian oscillator. However, in some large single cell algae, the nucleus can be removed and the circadian oscillation persists for many days. Our reseach is aimed at determining the mechanism of the oscillation in these algae. It appears that, perhaps, there is some long lived mRNA that is involved in the rhythm generation. In any case, the feedback cannot be at the mRNA synthesis step. It may be at the protein synthesis step. Techniques involving mutagens, x-rays, and chemicals which affect protein synthesis are being used to determine the steps involved in generating the rhythm in these algae. Such steps may be involved in generating oscillations in other organisms. We are also using the polymerase chain reaction technique to look for similarities of genes from this alga and known circadian genes from other organisms.