Fecundity and fertility in the amphipod Echinogammarus marinus (Leach) were investigated at 2 industrially contaminated sites and compared with data from 2 reference sites. Although some studies have used amphipod fecundity or fertility as biomarkers of environmental perturbation, there has been very little standardisation with regard to the endpoints quantified. Mean brood size, brood size normalised to female weight, and embryos in early and late stages of development have been utilised as measures of amphipod fecundity and fertility. The present study examined the effectiveness of all these measures as biomarkers of pollution. The results suggest that different interpretations can be derived depending on the measure used to express fecundity or fertility. Compared with impacted sites, only reference sites had larger broods normalised to female weight. Separating early- and late-egg developmental stages provided additional information as to whether initial fecundity, or relative fertility, was being affected compared with pooled data (all embryo stages). Both reference sites produced more eggs in early stages of development than impacted sites, but only 1 impacted site had fewer embryo numbers at later stages of development. These results indicate that separating embryo stages in field monitoring or laboratory studies provides more effective indicators of reproductive endpoints, and misinterpretations may result if the loss of eggs and/or embryos from the brood chamber is not taken into consideration.