It has been suggested that Merino sheep with flighty temperament are more susceptible to internal parasite infection. This hypothesis was further tested in this study using data from the Sheep Genomics Falkiner Memorial Field Station Flock. Genotypic and phenotypic parameters and heritabilities for temperament, measured as flight time and agitation score, and internal parasite resistance, measured as worm egg counts from 'Haemonchus contortus' and 'Trichostrongylus colubriformis' challenges were estimated. Heritabilities for the traits examined were moderate with the exception of flight time, which was low (h² flight = 0.07 ± 0.04). The heritability of agitation score was estimated at 0.21 ± 0.05. Worm egg count heritabilities ranged from 0.13 to 0.30, and were lowest in the 'T. colubriformis' challenge. Genetic correlations between worm egg counts and agitation score were generally moderately negative (rg = -0.16 to -0.21); the exception was the first count from the 'T. colubriformis' challenge. Genetic correlations of worm egg counts with flight time were lower than with agitation score, the exception was Twec2 which was higher (rg = -0.30). All genetic correlations were associated with high standard errors. Our results suggest that animals with faster flight times and/or low agitation score may have higher WEC scores following a nematode challenge. Further research is needed to validate the existence of such as relationship.