(1) Changes in the arthropod fauna of a newly established ley pasture were monitored in soil and vegetation. Soil and foliage communities increased in species richness during the 3-year study. Numbers in the soil to a depth of 5 cm increased in each successive year from 2317 to 114 413 individuals m$^{-2}$. However, most groups extracted from the foliage by Tullgren funnel showed no significant change in abundance. (2) Various groups collected in suction net samples exhibited contrasting population trends. Insect numbers attained a late summer peak which became greater in successive years. Numbers of Cryptostigmata increased steadily throughout the study. Detritivorous Collembola exhibited population minima in midsummer when phytophagous species attained peak abundance. (3) A graphical method of tracing the accumulation of species in small samples was more useful for quantifying changes in the faunal complexity of the study site than were conventional indices of diversity.