Fucus vesiculosus,F.evanescens, andAscophyllum nodosumhave been analyzed monthly for their content of moisture, mineral salts, organic nitrogen, mannitol, laminarin, and alginate over a period of two years. Plants were collected from two localities, St. Andrews, N.B., and Halifax, N.S. In general, when the ash content was at a minimum in the winter months, alginate was at a maximum. The converse was true in spring and summer. Organic nitrogen and laminarin remained relatively constant throughout the year. Mannitol was highest in the summer and autumn, fluctuating with the temperature of the water. No essential difference was detected between the results of St. Andrews and at Halifax, or between the three species examined. Analyses carried out on samples collected at different times on the same day showed no significant differences.