Let a random directed acyclic graph be defined as being obtained from the random graph Gn, p by orienting the edges according to the ordering of vertices. Let γn* be the size of the largest (reflexive, transitive) closure of a vertex. For p=c(log n)/n, we prove that, with high probability, γn* is asymptotic to nc log n, 2n(log log n)/log n, and n(1−1/c) depending on whether c<1, c=1, or c>1. We also determine the limiting distribution of the first vertex closure in all three ranges of c. As an application, we show that the expected number of comparable pairs is asymptotic to n1+c/c log n, ½(n(log log n)/log n)2, and ½(n(1−1/c))2, respectively. © 2001 John Wiley & Sons, Inc. Random Struct. Alg., 18: 164–184, 2001