WordNet (r) 3.0 (2006):

follow up
    v 1: pursue to a conclusion or bring to a successful issue; "Did
         he go through with the treatment?"; "He implemented a new
         economic plan"; "She followed up his recommendations with a
         written proposal" [syn: follow through, follow up,
         follow out, carry out, implement, put through, go
         through]
    2: increase the effectiveness or success of by further action;
       "The doctor followed up the surgery with radiation"

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "follow up":
   PS, Parthian shot, addendum, afterthought, anamnesis, appendix,
   associative anamnesis, attend, back matter, carry through,
   case history, catamnesis, chase, chivy, chorus, coda, codicil,
   colophon, come after, conclusion, consequence, continuance,
   continuation, displace, dog, dogging, double take, dying words,
   emanate, ensue, envoi, epilogue, exhaust every move, follow,
   follow a clue, follow after, follow out, follow through,
   follow-through, following, give chase, go after, go all lengths,
   go all out, go for broke, go the limit, hollo after, hound,
   hue and cry, hunt, hunt down, hunting, issue, last words,
   leave nothing undone, make after, medical history, nose, nose out,
   overlook nothing, overtake, parting shot, peroration, postface,
   postfix, postlude, postscript, prosecute, prosecution, pursuance,
   pursue, pursuing, pursuit, quest, quest after, raise the hunt,
   refrain, replace, result, run after, run down, run to earth,
   search, searching, second thought, see it through, see out, seek,
   seek out, seeking, sequel, sequela, sequelae, sequelant, sequent,
   sequitur, shadow, shadowing, smell out, sniff out, stalk, stalking,
   subscript, succeed, suffix, supervene, supplement, swan song, tag,
   tail, take out after, trace, trace down, track, track down,
   tracking, tracking down, trail, trailing