In this paper the 3-way intersection problem for S(2,4,v) designs is
investigated. Let bv=12v(v−1) and
I3[v]={0,1,...,bv}∖{bv−7,bv−6,bv−5,bv−4,bv−3,bv−2,bv−1}.
Let J3[v]={k∣ there exist three S(2,4,v) designs with k same common
blocks}. We show that J3[v]⊆I3[v] for any positive integer
v≡1,4 (mod 12) and J3[v]=I3[v], for v≥49 and v=13. We find J3[16] completely. Also we determine some values of J3[v]
for v=25,28,37 and 40.