The diagnostic significance of immediate reaction (IR) and late-phase skin reaction (LPR) in early infancy was evaluated. Twenty six infants aged 3 months, with atopic dermatitis, received an intracutaneous test injection of egg white extract or control solution. Total serum IgE levels, peripheral eosinophile counts, CAP-RAST scores, and lymphocyte stimulation tests (LST) with egg white extract were measured. Infants were tested and followed every 3 months up to 12 months of age. There was a significant relationship between the diameter of IR elicited by intracutaneous injection of egg white extract and total serum IgE levels (p < 0.01). The diameters of IR and the diameters of LPR did not correlate. In some cases, flares over 10 mm appeared 15 minutes after injection of control solution. The average serum IgE level in the IR-positive group tended to be higher than that in the IR-negative group but this difference was not statistically significant. The stimulation index (SI) of LST in the LPR-positive group was significantly higher than that in the control group (p < 0.05). In the RAST-positive group more cases had the acute symptoms provoked by egg ingestion at 12 months of age as compared to the RAST-negative group (p < 0.05). And in the IR-positive group also more cases had the symptoms than in the IR-negative group (p < 0.01). For infants aged 3 and 6 months the number of cases with positive RAST scores following injection of egg white extract was significantly higher in the IR-positive group than in the IR-negative group (p < 0.005, p < 0.05). There was no significant difference of the RAST positive ratio between the LPR-positive and the LPR-negative group. At 6 months of age, there were more cases with positive RAST scores in the IR- and/or LPR-positive group than in the group negative for both (p < 0.05). In the LPR-positive group more cases had symptoms of allergic bronchitis or bronchial asthma before 12 months of age as compared to the LPR-negative group (p < 0.005).