Barnacle pheromone enhances the rate of settlement and metamorphosis of larvae of Balanus amphitrite Darwin. Analogs to the heterogenous pheromone peptides were sought. Settlement assays were used to assess both the pheromone and the potential analogs. The pheromone has a lower threshold of activity at a concentration of 0.2 micrograms BSA protein equivalence l-1. Treatment with carboxypeptidase eliminates biological activity. Series of dipeptides were tested to determine if dipeptides could promote settlement. Combinations of acidic, neutral, and basic amino acids in dipeptides were examined. Specific small peptides can mimic barnacle pheromone. Only peptides with a basic carboxy-terminal amino acid and either a neutral or a basic amino-terminal amino acid enhance settlement. Six peptides were shown to mimic pheromone activity at concentrations comparable to the native molecule. Some peptides were more potent than others. The most effective peptides were L-leucyl-L-arginine and L-histidyl-L-lysine which had a lower threshold of settlement enhancement of 2.0 x 10(-10) M and caused a 130% increase in settlement rate at 2.0 x 10(-8) M. Glycyl-glycyl-L-arginine, glycyl-L-histidyl-L-lysine, L-leucyl-glycyl-L-arginine and L-tyrosyl-L-arginine had thresholds between 2.0 x 10(-8) M and 2.0 x 10(-9) M. Peptide pheromone analogs should be useful in determining the nature and mechanism of barnacle pheromone receptor interactions.