Two commercially available seaweed products, derived from Ascophyllum nodosum (An) and Ecklonia maxima (Em), were evaluated for their potential as control agents for the root-knot nematodes, Meloidogyne chitwoodi and Meloidogyne hapla. The effects of both products on hatching, host location and penetration by second-stage juveniles (J2) were examined. Continuous exposure of M. chitwoodi egg masses to 50 and 100 % An significantly reduced the final percentage hatch, but this result could not be confirmed. In a bioassay with pluronic gel, more J2 of M. chitwoodi and M. hapla were found within the 0.5-cm vicinity of a tomato root tip after 24- and 6-h pre-exposures to Em, respectively. On agar plates, J2 of M. chitwoodi pre-exposed to An or Em showed less attraction to tomato root diffusate compared with distilled water (DW). Moreover, J2 pre-exposed to An lost the ability to differentiate repellent and attractant solutions on agar plates, unlike J2 pre-exposed to Em or DW. A 24-h pre-exposure to An reduced the infectivity of M. chitwoodi and M. hapla, whereas pre-exposure to Em enhanced the infectivity of M. chitwoodi. In a glasshouse pot experiment, treatments with Em reduced M. hapla multiplication on tomato. For M. chitwoodi, no effect on the number of nematodes per gram root was seen. The root biomass significantly reduced for untreated plants infested with M. chitwoodi compared to Em- and An-treated plants. The results indicate that these seaweed products adversely affect hatching and sensory perception in in vitro assays, but assumptions about in vivo effects may be unwise as dilutions of the products when applied as soil drenches may compromise activity.