Relationships between physiological variables of middle and late post-hatch broilers with their corresponding egg and embryo variables were examined. Sixty Ross×Ross 708 broiler hatching eggs were randomly set on each of 8 replicate tray levels of an incubator. On 10.5 d of incubation, transponders were implanted in the air cells of 4 embryonated eggs per replicate for determination of internal egg temperature (T_emb) through d 18.5. On d 18.5, the implanted embryonated eggs were transferred to a hatcher unit where they were monitored for hatch every 12 h. Incubation length, eggshell water vapor conductance (G_H2O), specific G_H2O (g_H2O; G_H2O adjusted to a 100 g set egg weight basis), and G_H2O constants (K_H2O) of the embryonated eggs were determined. Chicks were placed in corresponding replicate floor pens and were grown out from 0 (21.5 d of incubation) to 48 d of age. On 28 and 48 d post-hatch, approximately 2 birds per pen were necropsied for determination of BW, and the relative weights and moisture concentrations of their liver, breast muscle, and left gastrocnemius muscle. Breast muscle moisture concentration on d 28 was negatively correlated with G_H2O, g_H2O, and K_H2O, and breast muscle moisture concentration on d 48 was negatively correlated with incubation length. However, relative body and breast muscle weights on d 48 were positively correlated with g_H2O and K_H2O, and relative BW on d 48 was positively correlated with incubation length. More importantly, relative breast muscle weight on d 48 post-hatch was negatively correlated with T_emb. The variables T_emb, G_H2O, g_H2O, and K_H2O may differentially influence the physiological variables in birds during the middle and late post-hatch grow out periods, and bird metabolic and hydration statuses may be adjusted later during the post-hatch period, so that bird BW will eventually reach its genetically predetermined level.