I have set the spacing after subsubsection to 1sp, but there is still an appreciable space between the heading and the text (approx 1ex). Obviously, I can't set a negative value, and I don't want to manually create a negative space at the start of every subsubsection.
Any suggestions on how to do this? Is there a length variable that I should be setting?
\documentclass[10pt,letterpaper]{article}
\usepackage[letterpaper,margin=0.75in]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{mdwlist}
\usepackage[T1]{fontenc}
\usepackage{textcomp}
\usepackage{tgpagella}
\pagestyle{empty}
\begin{document}
\setlength{\parskip}{0em}
\setlength{\parindent}{0em}
\makeatletter
\renewcommand\paragraph{\@startsection{paragraph}{4}{\z@}%
{1.25ex \@plus1ex \@minus.2ex}%
{-0em}%
{\normalfont\normalsize\bfseries}}
\renewcommand\subsubsection{\@startsection {subsubsection}{3}{\z@ }%
{-1.5ex\@plus -1ex \@minus -.2ex}%
{1sp \@minus 1ex}%
{\normalfont \normalsize \bfseries }}
\makeatother
\subsubsection*{Blah}
This text is 1ex from the heading blah, but I would like it to be hard up
against the heading (but not on the same line)
\end{document}
I need to be able to have some headings which have some space, and some which have none, so I can't use a package which simply affects the whole document.

1exspace that remains after setting the vertical spacing to1spin thesubsubsectioncommand. – Marcin Jul 28 '12 at 15:16\renewcommand\subsubsection{\offinterlineskip\@startsection {subsubsection}{3}{\z@ } {-1.5ex\@plus -1ex \@minus -.2ex} {1sp \@minus 1ex} {\normalfont \normalsize \bfseries }}– Gonzalo Medina Jul 28 '12 at 15:58\offinterlineskip. Go ahead and post that as an answer with a description of what it does, and I'll vote it up. Update: testing shows that that still leaves a gap (albeit slightly smaller). Sorry. – Marcin Jul 28 '12 at 17:12