Life-history traits were studied in one marine and four fresh-water shrimps from tropical regions of western South America: Palaemon northropi, P. pandaliformis, Macrobrachium acanthurus, and M. olfersi (Palaemonidae). Occasional data are given for Macrobrachium carcinus and an atyid shrimp, Potimirim potimirim. Size was measured as total body length (TBL), carapace length (CL), and telson length (TL), weight as dry weight (W), and realized fecundity as number of eggs per female. Size and W of eggs were determined in an early stage of development. Relationships between measurements of size, weight, and fecundity are described with regression equations. Significant species- and sex-specific variation was found in the slopes of the allometric TBL-W relationship. In the 2 species of Palaemon, females grew to a larger size than males; they showed also a steeper W increase with increasing TBL. Opposite patterns were observed in M. acanthurus and M. olfersii, suggesting different traits on the generic level. The minimum sexable size (minimum size of males with appendix masculina) was unrelated to the species-specific maximum size. Size at the onset of female maturity (minimum size with eggs) was larger in M. acanthurus than in the other species (29 versus 20-22 mm); W at the onset of female maturity increased with the maximum size of a species. Regressions of egg number on TBL indicated the highest overall level as well as the strongest size-dependence of fecundity in M. olfersii; these parameters were lowest in P. pandaliformis. The reproductive output (RO:W of egg mass in relation to female body W) was lowest in the only marine species studies here, P. northropi (14.4 versus 18.6-21.7%). With the possible exception of the RO, the life-history traits of these tropical shrimps appear unrelated to the climatic origin or habitat of a species.