Total and differential leukocyte count profiles were studied in 62 clinically healthy Danish landrace kids and 34 clinically healthy dwarf kids from birth to 12 months of age in seven Danish herds. The objective was to determine the reference values in the two breeds and the influence of age, sex and environment and whether there are any breed differences. Parametric (mean +/- 2 standard deviations) and the nonparametric (5th to 95th percentile interval) values for each leukocyte type were closely related. The medians were very close to the means. The number of leukocytes was low in neonates, 7.1 +/- 1.5 and 7.0 +/- 2.1 x 10(9)/l in dwarf and landrace kids respectively. Values increased with age to 18.7 +/- 2.1 and 13.4 +/- 3.1 x 10(9)/l in the two breeds respectively at 8-12 months of age. There were significant differences in leukocyte counts between the breeds at 1-2 and 8-12 months of age and at 2-4 months between herds within the breeds. The number of lymphocyte and neutrophil cells were 2.6 +/- 0.8 and 3.9 +/- 1.1 x 10(9)/l respectively in neonatal dwarf and 4.1 +/- 1.5 and 2.3 +/- 1.1 x 10(9)/l respectively in landrace kids. Very high numbers of these cells were observed in dwarf and landrace kids respectively within 8 months, 10.7 +/- 1.1 and 8.2 +/- 3.3 lymphocytes and 6.8 +/- 1.7 and 4.4 +/- 2.6 x 10(9)/l neutrophils for the two breeds. Significant differences between the ages (within the breeds), breeds (within similar ages) and herds (within breeds in kids of similar ages) were observed.(ABSTRACT TRUNCATED AT 250 WORDS)